https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116912
Bug ID: 116912
Summary: Cross-compiling aarch64 on x86_64 incorrectly
ignores/discards function output parameter
Product: gcc
Version: 13.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: rtl-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: seanjc at google dot com
Target Milestone: ---
Created attachment 59242
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=59242&action=edit
Intermediate output of the miscompiled file
aarch64-linux-gnu-gcc 13.2.0 and 11.4.0 (haven't tried other gcc versions) on
x86-64 miscompile this code snippet:
static noinline void set_pmcr_n(uint64_t *pmcr, uint64_t pmcr_n)
{
u64p_replace_bits((__u64 *) pmcr, pmcr_n, ARMV8_PMU_PMCR_N);
}
pmcr = pmcr_orig;
printf("orig = %lx, next = %lx, want = %lu\n", pmcr_orig, pmcr,
pmcr_n);
set_pmcr_n(&pmcr, pmcr_n);
printf("orig = %lx, next = %lx, want = %lu\n", pmcr_orig, pmcr,
pmcr_n);
into code the ignores the @pmcr output parameter. The generated code for
set_pmcr_n() is correct, the caller simply ignores the result that is stored
into @pmcr. Note, the printf() calls aren't necessary to reproduce the issue,
they were added purely to serve as markers to make it easy to visually confirm
the issue. There is other consumption of the set_pmcr_n() output that also
ignores the result (the issue originally manifested as a failed test).
E.g. aarch64-linux-gnu-gcc 13.2.0 generates:
0000000000401c90 <set_pmcr_n>:
401c90: f9400002 ldr x2, [x0]
401c94: b3751022 bfi x2, x1, #11, #5
401c98: f9000002 str x2, [x0]
401c9c: d65f03c0 ret
0000000000402660 <test_create_vpmu_vm_with_pmcr_n>:
...
402724: aa1403e3 mov x3, x20
402728: aa1503e2 mov x2, x21
40272c: aa1603e0 mov x0, x22
402730: aa1503e1 mov x1, x21
402734: 940060ff bl 41ab30 <_IO_printf>
402738: aa1403e1 mov x1, x20
40273c: 910183e0 add x0, sp, #0x60
402740: 97fffd54 bl 401c90 <set_pmcr_n>
402744: aa1403e3 mov x3, x20
402748: aa1503e2 mov x2, x21
40274c: aa1503e1 mov x1, x21
402750: aa1603e0 mov x0, x22
402754: 940060f7 bl 41ab30 <_IO_printf>
and running the compiled program with a value of pmcr_n=6 yields output of:
orig = 3040, next = 3040, want = 0
orig = 3040, next = 3040, want = 0
$ aarch64-linux-gnu-gcc -v
Using built-in specs.
COLLECT_GCC=aarch64-linux-gnu-gcc
COLLECT_LTO_WRAPPER=/usr/libexec/gcc-cross/aarch64-linux-gnu/13/lto-wrapper
Target: aarch64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Debian 13.2.0-13'
--with-bugurl=file:///usr/share/doc/gcc-13/README.Bugs
--enable-languages=c,ada,c++,go,d,fortran,objc,obj-c++,m2 --prefix=/usr
--with-gcc-major-version-only --program-suffix=-13 --enable-shared
--enable-linker-build-id --libexecdir=/usr/libexec --without-included-gettext
--enable-threads=posix --libdir=/usr/lib --enable-nls --with-sysroot=/
--enable-clocale=gnu --enable-libstdcxx-debug --enable-libstdcxx-time=yes
--with-default-libstdcxx-abi=new --enable-libstdcxx-backtrace
--enable-gnu-unique-object --disable-libquadmath --disable-libquadmath-support
--enable-plugin --enable-default-pie --with-system-zlib
--enable-libphobos-checking=release --without-target-system-zlib
--enable-multiarch --enable-fix-cortex-a53-843419 --disable-werror
--enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu
--target=aarch64-linux-gnu --program-prefix=aarch64-linux-gnu-
--includedir=/usr/aarch64-linux-gnu/include
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 13.2.0 (Debian 13.2.0-13)
