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Fix iconv build with GCC mainline

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Current GCC mainline produces -Wstringop-overflow errors building some
iconv converters, as discussed at
<https://gcc.gnu.org/pipermail/gcc/2021-July/236943.html>.  Add an
__builtin_unreachable call as suggested so that GCC can see the case
that would involve a buffer overflow is unreachable; because the
unreachability depends on valid conversion state being passed into the
function from previous conversion steps, it's not something the
compiler can reasonably deduce on its own.

Tested with build-many-glibcs.py that, together with
<https://sourceware.org/pipermail/libc-alpha/2021-August/130244.html>,
it restores the glibc build for powerpc-linux-gnu.
This commit is contained in:
Joseph Myers 2021-08-23 16:18:42 +00:00
parent a4f5a3103f
commit c8126360df
1 changed files with 6 additions and 0 deletions
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6
iconv/loop.c
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@ -436,6 +436,12 @@ SINGLE(LOOPFCT) (struct __gconv_step *step,
return __GCONV_FULL_OUTPUT;
/* Now add characters from the normal input buffer. */
if (inlen >= MAX_NEEDED_INPUT)
/* Avoid a -Wstringop-overflow= warning when this loop is
unrolled. The compiler cannot otherwise see that this is
unreachable because it depends on (state->__count & 7) not
being too large after a previous conversion step. */
__builtin_unreachable ();
do
bytebuf[inlen++] = *inptr++;
while (inlen < MAX_NEEDED_INPUT && inptr < inend);