On Sun, 24 May 2020, Carl Eugen Hoyos wrote:
Am Sa., 23. Mai 2020 um 20:35 Uhr schrieb Martin Storsjö <mar...@martin.st>:
The cabac inline assembly is very brittle to assemble properly
on i386 windows with clang; libavcodec/hevc_cabac.c fails to build
in the default mode (which is -march=pentium4), it only works if
ffmpeg is configured with --cpu=i686 (translating to -march=i686),
and likewise, the inline assembly fails to assemble in
libavcodec/h264_cabac.c if building with optimizations disabled.
Instead of trying to step around the problem (and end up bit by it
occasionally), just disable the inline assembly for this configuration.
I think I cannot reproduce this issue, what may I miss?
That's a good question - how are you building? I can reproduce it both in
mingw and msvc mode.
In mingw mode (with my llvm-mingw toolchains from
https://github.com/mstorsjo/llvm-mingw, but any clang configured to target
i386 mingw should do), I can reproduce it (in a cross compile setup) like
this (tested with Clang 10.0 but any version should do, I remember seeing
the issue long ago):
$ configure --cross-prefix=i686-w64-mingw32- --target-os=mingw32
--arch=i686 --enable-gpl
$ make V=1
...
i686-w64-mingw32-gcc -I. -Isrc/ -D_ISOC99_SOURCE -D_FILE_OFFSET_BITS=64
-D_LARGEFILE_SOURCE -U__STRICT_ANSI__ -D__USE_MINGW_ANSI_STDIO=1
-D_POSIX_C_SOURCE=200112 -D_XOPEN_SOURCE=600 -DHAVE_AV_CONFIG_H
-DBUILDING_avcodec -std=c11 -fomit-frame-pointer -g
-Wdeclaration-after-statement -Wall -Wdisabled-optimization
-Wpointer-arith -Wredundant-decls -Wwrite-strings -Wtype-limits -Wundef
-Wmissing-prototypes -Wno-pointer-to-int-cast -Wstrict-prototypes
-Wempty-body -Wno-parentheses -Wno-switch -Wno-format-zero-length
-Wno-pointer-sign -Wno-unused-const-variable -Wno-bool-operation
-Wno-char-subscripts -O3 -fno-math-errno -fno-signed-zeros
-Qunused-arguments -Werror=implicit-function-declaration
-Werror=missing-prototypes -Werror=return-type -MMD -MF
libavcodec/hevc_cabac.d -MT libavcodec/hevc_cabac.o -c -o
libavcodec/hevc_cabac.o src/libavcodec/hevc_cabac.c
warning: unknown warning option '-Wno-bool-operation'; did you mean
'-Wno-bool-conversion'? [-Wunknown-warning-option]
src/libavcodec/hevc_cabac.c:37:21: warning: variable 'num_bins_in_se' is
not needed and will not be emitted [-Wunneeded-internal-declaration]
static const int8_t num_bins_in_se[] = {
^
In file included from src/libavcodec/hevc_cabac.c:27:
In file included from src/libavcodec/cabac_functions.h:46:
src/libavcodec/x86/cabac.h:193:9: error: inline assembly requires more
registers than available
BRANCHLESS_GET_CABAC("%0", "%q0", "(%4)", "%1", "%w1",
^
Same thing if I build in MSVC mode, by setting INCLUDE and LIB to point to
the right MSVC folders, and configure like this:
$ configure --enable-gpl --arch=i686 --cc='clang -target i686-win32-msvc'
--ld=lld-link --target-os=win32 --extra-ldflags='msvcrt.lib oldnames.lib'
--enable-cross-compile --ar=llvm-ar --nm=llvm-nm --disable-stripping
$ make V=1
clang -target i686-win32-msvc -I. -Isrc/ -D_ISOC99_SOURCE
-D_FILE_OFFSET_BITS=64 -D_LARGEFILE_SOURCE -D_USE_MATH_DEFINES
-D_CRT_SECURE_NO_WARNINGS -D_CRT_NONSTDC_NO_WARNINGS -D_WIN32_WINNT=0x0600
-DHAVE_AV_CONFIG_H -DBUILDING_avcodec -std=c11 -fomit-frame-pointer -g
-Wdeclaration-after-statement -Wall -Wdisabled-optimization
-Wpointer-arith -Wredundant-decls -Wwrite-strings -Wtype-limits -Wundef
-Wmissing-prototypes -Wno-pointer-to-int-cast -Wstrict-prototypes
-Wempty-body -Wno-parentheses -Wno-switch -Wno-format-zero-length
-Wno-pointer-sign -Wno-unused-const-variable -Wno-bool-operation
-Wno-char-subscripts -O3 -fno-math-errno -fno-signed-zeros
-Qunused-arguments -Werror=implicit-function-declaration
-Werror=missing-prototypes -Werror=return-type -MMD -MF
libavcodec/hevc_cabac.d -MT libavcodec/hevc_cabac.o -c -o
libavcodec/hevc_cabac.o src/libavcodec/hevc_cabac.c
src/libavcodec/hevc_cabac.c:37:21: warning: variable 'num_bins_in_se' is
not needed and will not be emitted [-Wunneeded-internal-declaration]
static const int8_t num_bins_in_se[] = {
^
In file included from src/libavcodec/hevc_cabac.c:27:
In file included from src/libavcodec/cabac_functions.h:46:
src/libavcodec/x86/cabac.h:193:9: error: inline assembly requires more
registers than available
BRANCHLESS_GET_CABAC("%0", "%q0", "(%4)", "%1", "%w1",
^
The same also seems to trigger in the same way if using the clang-cl
frontend, e.g. configured like this:
configure --enable-gpl --arch=i686 --cc=clang-cl --ld=lld-link
--target-os=win32 --toolchain=msvc --enable-cross-compile --ar=llvm-ar
--nm=llvm-nm --disable-stripping --extra-cflags=-m32
In the first two cases, adding --cpu=i686 to the configure line, which
converts into -march=i686 on the compile commands, makes the issue go
away. For clang-cl, --cpu=i686 doesn't have any effect, so the issue
doesn't easily go away there.
Now if configuring with --cpu=i686 --disable-optimizations, the same
issues are back again, in both libavcodec/h264_cabac.o and
libavcodec/hevc_cabac.o.
// Martin
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