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On reflection (especially after noticing how many buildfarm critters have __builtin_types_compatible_p but not _Static_assert), it seems like we ought to try a bit harder to make these macros do something everywhere. The initial cut at it would have been no help to code that is compiled only on platforms without _Static_assert, for instance; and in any case not all our contributors do their initial coding on the latest gcc version. Some googling about static assertions turns up quite a bit of prior art for making it work in compilers that lack _Static_assert. The method that seems closest to our needs involves defining a struct with a bit-field that has negative width if the assertion condition fails. There seems no reliable way to get the error message string to be output, but throwing a compile error with a confusing message is better than missing the problem altogether. In the same spirit, if we don't have __builtin_types_compatible_p we can at least insist that the variable have the same width as the type. This won't catch errors such as "wrong pointer type", but it's far better than nothing. In addition to changing the macro definitions, adjust a compile-time-constant Assert in contrib/hstore to use StaticAssertStmt, so we can get some buildfarm coverage on whether that macro behaves sanely or not. There's surely more places that could be converted, but this is the first one I came across.
370 lines
10 KiB
C
370 lines
10 KiB
C
/*
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* contrib/hstore/hstore_compat.c
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*
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* Notes on old/new hstore format disambiguation.
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*
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* There are three formats to consider:
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* 1) old contrib/hstore (referred to as hstore-old)
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* 2) prerelease pgfoundry hstore
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* 3) new contrib/hstore
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*
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* (2) and (3) are identical except for the HS_FLAG_NEWVERSION
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* bit, which is set in (3) but not (2).
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*
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* Values that are already in format (3), or which are
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* unambiguously in format (2), are handled by the first
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* "return immediately" test in hstoreUpgrade().
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*
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* To stress a point: we ONLY get here with possibly-ambiguous
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* values if we're doing some sort of in-place migration from an
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* old prerelease pgfoundry hstore-new; and we explicitly don't
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* support that without fixing up any potentially padded values
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* first. Most of the code here is serious overkill, but the
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* performance penalty isn't serious (especially compared to the
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* palloc() that we have to do anyway) and the belt-and-braces
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* validity checks provide some reassurance. (If for some reason
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* we get a value that would have worked on the old code, but
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* which would be botched by the conversion code, the validity
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* checks will fail it first so we get an error rather than bad
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* data.)
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*
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* Note also that empty hstores are the same in (2) and (3), so
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* there are some special-case paths for them.
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*
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* We tell the difference between formats (2) and (3) as follows (but
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* note that there are some edge cases where we can't tell; see
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* comments in hstoreUpgrade):
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*
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* First, since there must be at least one entry, we look at
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* how the bits line up. The new format looks like:
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*
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* 10kkkkkkkkkkkkkkkkkkkkkkkkkkkkkk (k..k = keylen)
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* 0nvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv (v..v = keylen+vallen)
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*
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* The old format looks like one of these, depending on endianness
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* and bitfield layout: (k..k = keylen, v..v = vallen, p..p = pos,
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* n = isnull)
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*
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* kkkkkkkkkkkkkkkkvvvvvvvvvvvvvvvv
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* nppppppppppppppppppppppppppppppp
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*
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* kkkkkkkkkkkkkkkkvvvvvvvvvvvvvvvv
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* pppppppppppppppppppppppppppppppn
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*
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* vvvvvvvvvvvvvvvvkkkkkkkkkkkkkkkk
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* nppppppppppppppppppppppppppppppp
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*
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* vvvvvvvvvvvvvvvvkkkkkkkkkkkkkkkk
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* pppppppppppppppppppppppppppppppn (usual i386 format)
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*
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* If the entry is in old format, for the first entry "pos" must be 0.
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* We can obviously see that either keylen or vallen must be >32768
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* for there to be any ambiguity (which is why lengths less than that
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* are fasttracked in hstore.h) Since "pos"==0, the "v" field in the
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* new-format interpretation can only be 0 or 1, which constrains all
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* but three bits of the old-format's k and v fields. But in addition
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* to all of this, the data length implied by the keylen and vallen
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* must fit in the varlena size. So the only ambiguous edge case for
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* hstores with only one entry occurs between a new-format entry with
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* an excess (~32k) of padding, and an old-format entry. But we know
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* which format to use in that case based on how we were compiled, so
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* no actual data corruption can occur.
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*
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* If there is more than one entry, the requirement that keys do not
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* decrease in length, and that positions increase contiguously, and
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* that the end of the data not be beyond the end of the varlena
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* itself, disambiguates in almost all other cases. There is a small
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* set of ambiguous cases which could occur if the old-format value
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* has a large excess of padding and just the right pattern of key
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* sizes, but these are also handled based on how we were compiled.
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*
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* The otherwise undocumented function hstore_version_diag is provided
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* for testing purposes.
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*/
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#include "postgres.h"
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#include "hstore.h"
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/*
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* This is the structure used for entries in the old contrib/hstore
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* implementation. Notice that this is the same size as the new entry
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* (two 32-bit words per key/value pair) and that the header is the
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* same, so the old and new versions of ARRPTR, STRPTR, CALCDATASIZE
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* etc. are compatible.
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*
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* If the above statement isn't true on some bizarre platform, we're
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* a bit hosed (see StaticAssertStmt in hstoreValidOldFormat).
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*/
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typedef struct
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{
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uint16 keylen;
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uint16 vallen;
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uint32
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valisnull:1,
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pos:31;
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} HOldEntry;
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static int hstoreValidNewFormat(HStore *hs);
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static int hstoreValidOldFormat(HStore *hs);
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/*
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* Validity test for a new-format hstore.
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* 0 = not valid
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* 1 = valid but with "slop" in the length
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* 2 = exactly valid
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*/
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static int
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hstoreValidNewFormat(HStore *hs)
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{
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int count = HS_COUNT(hs);
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HEntry *entries = ARRPTR(hs);
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int buflen = (count) ? HSE_ENDPOS(entries[2 * (count) - 1]) : 0;
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int vsize = CALCDATASIZE(count, buflen);
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int i;
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if (hs->size_ & HS_FLAG_NEWVERSION)
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return 2;
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if (count == 0)
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return 2;
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if (!HSE_ISFIRST(entries[0]))
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return 0;
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if (vsize > VARSIZE(hs))
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return 0;
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/* entry position must be nondecreasing */
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for (i = 1; i < 2 * count; ++i)
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{
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if (HSE_ISFIRST(entries[i])
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|| (HSE_ENDPOS(entries[i]) < HSE_ENDPOS(entries[i - 1])))
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return 0;
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}
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/* key length must be nondecreasing and keys must not be null */
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for (i = 1; i < count; ++i)
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{
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if (HS_KEYLEN(entries, i) < HS_KEYLEN(entries, i - 1))
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return 0;
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if (HSE_ISNULL(entries[2 * i]))
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return 0;
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}
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if (vsize != VARSIZE(hs))
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return 1;
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return 2;
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}
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/*
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* Validity test for an old-format hstore.
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* 0 = not valid
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* 1 = valid but with "slop" in the length
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* 2 = exactly valid
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*/
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static int
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hstoreValidOldFormat(HStore *hs)
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{
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int count = hs->size_;
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HOldEntry *entries = (HOldEntry *) ARRPTR(hs);
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int vsize;
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int lastpos = 0;
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int i;
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if (hs->size_ & HS_FLAG_NEWVERSION)
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return 0;
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/* New format uses an HEntry for key and another for value */
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StaticAssertStmt(sizeof(HOldEntry) == 2 * sizeof(HEntry),
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"old hstore format is not upward-compatible");
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if (count == 0)
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return 2;
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if (count > 0xFFFFFFF)
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return 0;
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if (CALCDATASIZE(count, 0) > VARSIZE(hs))
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return 0;
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if (entries[0].pos != 0)
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return 0;
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/* key length must be nondecreasing */
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for (i = 1; i < count; ++i)
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{
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if (entries[i].keylen < entries[i - 1].keylen)
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return 0;
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}
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/*
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* entry position must be strictly increasing, except for the first entry
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* (which can be ""=>"" and thus zero-length); and all entries must be
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* properly contiguous
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*/
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for (i = 0; i < count; ++i)
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{
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if (entries[i].pos != lastpos)
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return 0;
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lastpos += (entries[i].keylen
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+ ((entries[i].valisnull) ? 0 : entries[i].vallen));
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}
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vsize = CALCDATASIZE(count, lastpos);
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if (vsize > VARSIZE(hs))
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return 0;
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if (vsize != VARSIZE(hs))
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return 1;
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return 2;
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}
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/*
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* hstoreUpgrade: PG_DETOAST_DATUM plus support for conversion of old hstores
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*/
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HStore *
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hstoreUpgrade(Datum orig)
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{
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HStore *hs = (HStore *) PG_DETOAST_DATUM(orig);
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int valid_new;
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int valid_old;
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bool writable;
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/* Return immediately if no conversion needed */
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if ((hs->size_ & HS_FLAG_NEWVERSION) ||
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hs->size_ == 0 ||
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(VARSIZE(hs) < 32768 && HSE_ISFIRST((ARRPTR(hs)[0]))))
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return hs;
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valid_new = hstoreValidNewFormat(hs);
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valid_old = hstoreValidOldFormat(hs);
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/* Do we have a writable copy? */
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writable = ((void *) hs != (void *) DatumGetPointer(orig));
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if (!valid_old || hs->size_ == 0)
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{
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if (valid_new)
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{
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/*
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* force the "new version" flag and the correct varlena length,
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* but only if we have a writable copy already (which we almost
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* always will, since short new-format values won't come through
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* here)
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*/
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if (writable)
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{
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HS_SETCOUNT(hs, HS_COUNT(hs));
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HS_FIXSIZE(hs, HS_COUNT(hs));
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}
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return hs;
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}
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else
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{
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elog(ERROR, "invalid hstore value found");
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}
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}
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/*
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* this is the tricky edge case. It is only possible in some quite extreme
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* cases (the hstore must have had a lot of wasted padding space at the
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* end). But the only way a "new" hstore value could get here is if we're
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* upgrading in place from a pre-release version of hstore-new (NOT
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* contrib/hstore), so we work off the following assumptions: 1. If you're
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* moving from old contrib/hstore to hstore-new, you're required to fix up
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* any potential conflicts first, e.g. by running ALTER TABLE ... USING
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* col::text::hstore; on all hstore columns before upgrading. 2. If you're
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* moving from old contrib/hstore to new contrib/hstore, then "new" values
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* are impossible here 3. If you're moving from pre-release hstore-new to
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* hstore-new, then "old" values are impossible here 4. If you're moving
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* from pre-release hstore-new to new contrib/hstore, you're not doing so
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* as an in-place upgrade, so there is no issue So the upshot of all this
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* is that we can treat all the edge cases as "new" if we're being built
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* as hstore-new, and "old" if we're being built as contrib/hstore.
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*
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* XXX the WARNING can probably be downgraded to DEBUG1 once this has been
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* beta-tested. But for now, it would be very useful to know if anyone can
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* actually reach this case in a non-contrived setting.
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*/
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if (valid_new)
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{
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#if HSTORE_IS_HSTORE_NEW
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elog(WARNING, "ambiguous hstore value resolved as hstore-new");
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/*
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* force the "new version" flag and the correct varlena length, but
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* only if we have a writable copy already (which we almost always
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* will, since short new-format values won't come through here)
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*/
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if (writable)
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{
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HS_SETCOUNT(hs, HS_COUNT(hs));
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HS_FIXSIZE(hs, HS_COUNT(hs));
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}
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return hs;
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#else
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elog(WARNING, "ambiguous hstore value resolved as hstore-old");
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#endif
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}
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/*
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* must have an old-style value. Overwrite it in place as a new-style one,
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* making sure we have a writable copy first.
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*/
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if (!writable)
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hs = (HStore *) PG_DETOAST_DATUM_COPY(orig);
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{
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int count = hs->size_;
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HEntry *new_entries = ARRPTR(hs);
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HOldEntry *old_entries = (HOldEntry *) ARRPTR(hs);
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int i;
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for (i = 0; i < count; ++i)
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{
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uint32 pos = old_entries[i].pos;
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uint32 keylen = old_entries[i].keylen;
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uint32 vallen = old_entries[i].vallen;
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bool isnull = old_entries[i].valisnull;
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if (isnull)
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vallen = 0;
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new_entries[2 * i].entry = (pos + keylen) & HENTRY_POSMASK;
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new_entries[2 * i + 1].entry = (((pos + keylen + vallen) & HENTRY_POSMASK)
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| ((isnull) ? HENTRY_ISNULL : 0));
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}
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if (count)
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new_entries[0].entry |= HENTRY_ISFIRST;
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HS_SETCOUNT(hs, count);
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HS_FIXSIZE(hs, count);
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}
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return hs;
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}
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PG_FUNCTION_INFO_V1(hstore_version_diag);
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Datum hstore_version_diag(PG_FUNCTION_ARGS);
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Datum
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hstore_version_diag(PG_FUNCTION_ARGS)
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{
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HStore *hs = (HStore *) PG_DETOAST_DATUM(PG_GETARG_DATUM(0));
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int valid_new = hstoreValidNewFormat(hs);
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int valid_old = hstoreValidOldFormat(hs);
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PG_RETURN_INT32(valid_old * 10 + valid_new);
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}
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