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fast-export: use local array to store anonymized oid 

Some older versions of gcc complain about this line:

  builtin/fast-export.c:412:2: error: dereferencing type-punned pointer
       will break strict-aliasing rules [-Werror=strict-aliasing]
    put_be32(oid.hash + hashsz - 4, counter++);
    ^

This seems to be a false positive, as there's no type-punning at all
here. oid.hash is an array of unsigned char; when we pass it to a
function it decays to a pointer to unsigned char. We do take a void
pointer in put_be32(), but it's immediately aliased with another pointer
to unsigned char (and clearly the compiler is looking inside the inlined
put_be32(), since the warning doesn't happen with -O0).

This happens on gcc 4.8 and 4.9, but not later versions (I tested gcc 6,
7, 8, and 9).

We can work around it by using a local array instead of an object_id
struct. This is a little more intimate with the details of object_id,
but for whatever reason doesn't seem to trigger the compiler warning.
We can revert this patch once we decide that those gcc versions are too
old to care about for a warning like this (gcc 4.8 is the default
compiler for Ubuntu Trusty, which is out-of-support but not fully
end-of-life'd until April 2022).

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
maint
Jeff King 2020-06-25 15:48:37 -04:00 committed by Junio C Hamano
parent 8a49495583
commit f39ad38410
1 changed files with 4 additions and 4 deletions
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8
builtin/fast-export.c
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@ -405,12 +405,12 @@ static char *generate_fake_oid(void *data)
{
static uint32_t counter = 1; /* avoid null oid */
const unsigned hashsz = the_hash_algo->rawsz;
struct object_id oid;
unsigned char out[GIT_MAX_RAWSZ];
char *hex = xmallocz(GIT_MAX_HEXSZ);

oidclr(&oid);
put_be32(oid.hash + hashsz - 4, counter++);
return oid_to_hex_r(hex, &oid);
hashclr(out);
put_be32(out + hashsz - 4, counter++);
return hash_to_hex_algop_r(hex, out, the_hash_algo);
}

static const char *anonymize_oid(const char *oid_hex)