On Mon, Mar 31, 2014, at 0:37, Ralf Friedl wrote:
> >>> What's even worse is that adding any output to push(), even a puts("hi")
> >>> that does not print the argument or any of the stack vars, fixes it. So
> >>> something magic is going on inside the GCC optimization, I'm afraid this
> >>> is above my pay grade.
> >> Could you send the file miscutils/dc.o that is created with and without
> >> this puts("hi") in push()?
> > Attached.
> Are you using some special compiler options, especially regarding
> parameter passing in registers and stack alignment?
None, I'm afraid. CFLAGS etc are all unset. See later on for the gcc
defaults too.
Thanks for the research. I only speak x86 asm on a "yep, that's asm"
level.
> The instruction at 12 loads the double from address %edi after %edi has
> been set to point to the parameter area. The instruction at 0 in the
> failed case is exactly the same, except that %edi has not been setup
> before. So I would consider this a compiler bug.
Would it be possible for you to submit a gcc bug? I can try to do so
too, but it'll take a (long) while before I have time to build latest
gcc to test.
On bb side, I wonder if this gcc version should be blacklisted, or if
some workaround can be found.
Here's the -S -fverbose-asm output of an empty C file. I see nothing
about alignment, regparms, or otherwise relevant default options.
# GNU C (GCC) version 4.7.2 (i486-pc-linux-gnu)
# compiled by GNU C version 4.7.2, GMP version 5.1.1, MPFR version
3.1.1, MPC version 1.0.1
# GGC heuristics: --param ggc-min-expand=38 --param
ggc-min-heapsize=15472
# options passed:
# -iprefix
/tmp/tcloop/gcc/usr/local/bin/../lib/gcc/i486-pc-linux-gnu/4.7.2/
# test.c -mtune=i486 -march=i486 -fverbose-asm
# options enabled: -fauto-inc-dec -fbranch-count-reg -fcommon
# -fdebug-types-section -fdelete-null-pointer-checks -fdwarf2-cfi-asm
# -fearly-inlining -feliminate-unused-debug-types -ffunction-cse
-fgcse-lm
# -fgnu-runtime -fident -finline-atomics -fira-share-save-slots
# -fira-share-spill-slots -fivopts -fkeep-static-consts
# -fleading-underscore -fmath-errno -fmerge-debug-strings
# -fmove-loop-invariants -fpcc-struct-return -fpeephole
# -fprefetch-loop-arrays -fsched-critical-path-heuristic
# -fsched-dep-count-heuristic -fsched-group-heuristic -fsched-interblock
# -fsched-last-insn-heuristic -fsched-rank-heuristic -fsched-spec
# -fsched-spec-insn-heuristic -fsched-stalled-insns-dep -fshow-column
# -fsigned-zeros -fsplit-ivs-in-unroller -fstrict-volatile-bitfields
# -ftrapping-math -ftree-cselim -ftree-forwprop -ftree-loop-if-convert
# -ftree-loop-im -ftree-loop-ivcanon -ftree-loop-optimize
# -ftree-parallelize-loops= -ftree-phiprop -ftree-pta -ftree-reassoc
# -ftree-scev-cprop -ftree-slp-vectorize -ftree-vect-loop-version
# -funit-at-a-time -fvect-cost-model -fverbose-asm
# -fzero-initialized-in-bss -m32 -m80387 -m96bit-long-double
# -malign-stringops -mfancy-math-387 -mfp-ret-in-387 -mglibc -mieee-fp
# -mno-red-zone -mno-sse4 -mpush-args -msahf -mtls-direct-seg-refs
- Lauri
--
http://www.fastmail.fm - Faster than the air-speed velocity of an
unladen european swallow
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