[libc] Overflow error on riscv32 in strfrom functions

[mleleszi]

Looks like #166517 is breaking libc-riscv32-qemu-yocto-fullbuild-dbg build due to failing overflow test for strfrom.
https://lab.llvm.org/buildbot/#/changes/58668

int result = func(buff, sizeof(buff), "%.2147483647f", 1.0f);
EXPECT_LT(result, 0);
ASSERT_ERRNO_FAILURE();

[ RUN      ] LlvmLibcStrfromdTest.CharsWrittenOverflow
/home/libcrv32buildbot/bbroot/libc-riscv32-qemu-yocto-fullbuild-dbg/llvm-project/libc/test/src/stdlib/StrfromTest.h:493: FAILURE
       Expected: result
       Which is: 0
To be less than: 0
       Which is: 0
/home/libcrv32buildbot/bbroot/libc-riscv32-qemu-yocto-fullbuild-dbg/llvm-project/libc/test/src/stdlib/StrfromTest.h:494: FAILURE
          Expected: 0
          Which is: 0
To be not equal to: static_cast<int>(libc_errno)
          Which is: 0
[  FAILED  ] LlvmLibcStrfromdTest.CharsWrittenOverflow
Ran 8 tests.  PASS: 7  FAIL: 1

At first glance it seem like there is some kind of overflow in internal::strfromfloat_convert on 32bit archs because the other overflow test case is passing for snprintf. Interestingly, it passes on all other buildbots, including libc-arm32-qemu-debian-dbg.

This issue likely wasn't introduced by #166517 and was probably already present.

[llvmbot]

@llvm/issue-subscribers-libc

Author: Marcell Leleszi (mleleszi)

Looks like https://github.com//pull/166517 is breaking libc-riscv32-qemu-yocto-fullbuild-dbg build due to failing overflow test for strfrom. https://lab.llvm.org/buildbot/#/changes/58668

int result = func(buff, sizeof(buff), "%.2147483647f", 1.0f);
EXPECT_LT(result, 0);
ASSERT_ERRNO_FAILURE();

[ RUN      ] LlvmLibcStrfromdTest.CharsWrittenOverflow
/home/libcrv32buildbot/bbroot/libc-riscv32-qemu-yocto-fullbuild-dbg/llvm-project/libc/test/src/stdlib/StrfromTest.h:493: FAILURE
       Expected: result
       Which is: 0
To be less than: 0
       Which is: 0
/home/libcrv32buildbot/bbroot/libc-riscv32-qemu-yocto-fullbuild-dbg/llvm-project/libc/test/src/stdlib/StrfromTest.h:494: FAILURE
          Expected: 0
          Which is: 0
To be not equal to: static_cast<int>(libc_errno)
          Which is: 0
[  FAILED  ] LlvmLibcStrfromdTest.CharsWrittenOverflow
Ran 8 tests.  PASS: 7  FAIL: 1

At first glance it seem like there is some kind of overflow in internal::strfromfloat_convert on 32bit archs because the other overflow test case is passing for snprintf. Interestingly, it passes on all other buildbots, including libc-arm32-qemu-debian-dbg.

This issue likely wasn't introduced by #166517 and was probably already present.