On Thu, Nov 16, 2023 at 8:42 AM Dmitry Antipov <dmanti...@yandex.ru> wrote:
>
> (The following sample is taken from my LKML post at
> https://lkml.org/lkml/2023/11/15/213)
>
> $ cat t-build-bug.c
>
> struct vring_tx_mac {
> unsigned int d[3];
> unsigned int ucode_cmd;
> } __attribute__((packed));
>
> struct vring_rx_mac {
> unsigned int d0;
> unsigned int d1;
> unsigned short w4;
> union { struct { unsigned short pn_15_0; unsigned int pn_47_16; }
> __attribute__((packed));
> struct { unsigned short pn_15_0; unsigned int pn_47_16; }
> __attribute__((packed)) pn;
> };
> } __attribute__((packed));
>
> struct wil_ring_dma_addr {
> unsigned int addr_low;
> unsigned short addr_high;
> } __attribute__((packed));
>
> struct vring_tx_dma {
> unsigned int d0;
> struct wil_ring_dma_addr addr;
> unsigned char ip_length;
> unsigned char b11;
> unsigned char error;
> unsigned char status;
> unsigned short length;
> } __attribute__((packed));
>
> struct vring_tx_desc {
> struct vring_tx_mac mac;
> struct vring_tx_dma dma;
> } __attribute__((packed));
>
> struct wil_ring_tx_enhanced_mac {
> unsigned int d[3];
> unsigned short tso_mss;
> unsigned short scratchpad;
> } __attribute__((packed));
>
> struct wil_ring_tx_enhanced_dma {
> unsigned char l4_hdr_len;
> unsigned char cmd;
> unsigned short w1;
> struct wil_ring_dma_addr addr;
> unsigned char ip_length;
> unsigned char b11;
> unsigned short addr_high_high;
> unsigned short length;
> } __attribute__((packed));
>
> struct wil_tx_enhanced_desc {
> struct wil_ring_tx_enhanced_mac mac;
> struct wil_ring_tx_enhanced_dma dma;
> } __attribute__((packed));
>
> union wil_tx_desc {
> struct vring_tx_desc legacy;
> struct wil_tx_enhanced_desc enhanced;
> } __attribute__((packed));
>
> struct vring_rx_dma {
> unsigned int d0;
> struct wil_ring_dma_addr addr;
> unsigned char ip_length;
> unsigned char b11;
> unsigned char error;
> unsigned char status;
> unsigned short length;
> } __attribute__((packed));
>
> struct vring_rx_desc {
> struct vring_rx_mac mac;
> struct vring_rx_dma dma;
> } __attribute__((packed));
>
> struct wil_ring_rx_enhanced_mac {
> unsigned int d[3];
> unsigned short buff_id;
> unsigned short reserved;
> } __attribute((packed));
>
> struct wil_ring_rx_enhanced_dma {
> unsigned int d0;
> struct wil_ring_dma_addr addr;
> unsigned short w5;
> unsigned short addr_high_high;
> unsigned short length;
> } __attribute((packed));
>
> struct wil_rx_enhanced_desc {
> struct wil_ring_rx_enhanced_mac mac;
> struct wil_ring_rx_enhanced_dma dma;
> } __attribute((packed));
>
> union wil_rx_desc {
> struct vring_rx_desc legacy;
> struct wil_rx_enhanced_desc enhanced;
> } __attribute__((packed));
>
> union wil_ring_desc {
> union wil_tx_desc tx;
> union wil_rx_desc rx;
> } __attribute__((packed));
>
> int f (void) {
> return sizeof(union wil_ring_desc);
> }
>
> $ arm-linux-gnu-gcc -v
> Using built-in specs.
> COLLECT_GCC=arm-linux-gnu-gcc
> COLLECT_LTO_WRAPPER=/usr/libexec/gcc/arm-linux-gnueabi/13/lto-wrapper
> Target: arm-linux-gnueabi
> Configured with: ../gcc-13.2.1-20230728/configure --bindir=/usr/bin
> --build=x86_64-redhat-linux-gnu --datadir=/usr/share --disable-decimal-float
> --disable-dependency-tracking --disable-gold
> --disable-libgcj --disable-libgomp --disable-libmpx --disable-libquadmath
> --disable-libssp --disable-libunwind-exceptions --disable-shared
> --disable-silent-rules --disable-sjlj-exceptions
> --disable-threads --with-ld=/usr/bin/arm-linux-gnu-ld --enable-__cxa_atexit
> --enable-checking=release --enable-gnu-unique-object --enable-initfini-array
> --enable-languages=c,c++
> --enable-linker-build-id --enable-lto --enable-nls --enable-obsolete
> --enable-plugin --enable-targets=all --exec-prefix=/usr
> --host=x86_64-redhat-linux-gnu --includedir=/usr/include
> --infodir=/usr/share/info --libexecdir=/usr/libexec --localstatedir=/var
> --mandir=/usr/share/man --prefix=/usr --program-prefix=arm-linux-gnu-
> --sbindir=/usr/sbin --sharedstatedir=/var/lib
> --sysconfdir=/etc --target=arm-linux-gnueabi
> --with-bugurl=http://bugzilla.redhat.com/bugzilla/
> --with-gcc-major-version-only --with-isl --with-newlib
> --with-plugin-ld=/usr/bin/arm-linux-gnu-ld
> --with-sysroot=/usr/arm-linux-gnu/sys-root --with-system-libunwind
> --with-system-zlib --without-headers --with-tune=generic-armv7-a
> --with-arch=armv7-a --with-float=hard --with-fpu=vfpv3-d16
> --with-abi=aapcs-linux --enable-gnu-indirect-function
> --with-linker-hash-style=gnu
> Thread model: single
> Supported LTO compression algorithms: zlib zstd
> gcc version 13.2.1 20230728 (Red Hat Cross 13.2.1-1) (GCC)
>
> $ arm-linux-gnu-gcc -Os -c t-build-bug.c
> $ arm-linux-gnu-objdump -j .text -D t-build-bug.o
>
> t-build-bug.o: file format elf32-littlearm
>
> Disassembly of section .text:
>
> 00000000 <f>:
> 0: e3a00020 mov r0, #32 ;; As expected
> 4: e12fff1e bx lr
>
> ;; Now with a lot of weird things taken from the kernel's CFLAGS...
>
> $ arm-linux-gnu-gcc -mlittle-endian -std=gnu11 -fshort-wchar -funsigned-char
> -fno-common -fno-PIE -fno-strict-aliasing -fno-dwarf2-cfi-asm -mno-fdpic
> -fno-omit-frame-pointer -mapcs -mno-sched-prolog
> -fno-ipa-sra -mabi=apcs-gnu -mno-thumb-interwork -marm
> -Wa,-mno-warn-deprecated -march=armv4 -mtune=xscale -msoft-float -Uarm
> -fno-delete-null-pointer-checks -Os -fno-allow-store-data-races
> -fno-reorder-blocks -fno-ipa-cp-clone -fno-partial-inlining
> -fno-stack-protector -fno-omit-frame-pointer -fno-optimize-sibling-calls
> -ftrivial-auto-var-init=zero -fno-stack-clash-protection -pg
> -fno-inline-functions-called-once -fstrict-flex-arrays=3 -fno-strict-overflow
> -fno-stack-check -fconserve-stack -fsanitize=kernel-address
> -fasan-shadow-offset=0x1f000000 --param asan-globals=1 --param
> asan-instrumentation-with-call-threshold=10000 --param
> asan-instrument-allocas=1 --param asan-stack=1 --param
> asan-kernel-mem-intrinsic-prefix=1 -c t-build-bug.c
> $ arm-linux-gnu-objdump -j .text -D t-build-bug.o
>
> t-build-bug.o: file format elf32-littlearm
>
> Disassembly of section .text:
>
> 00000000 <f>:
> 0: e1a0c00d mov ip, sp
> 4: e92dd800 push {fp, ip, lr, pc}
> 8: e24cb004 sub fp, ip, #4
> c: e52de004 push {lr} @ (str lr, [sp, #-4]!)
> 10: ebfffffe bl 0 <__gnu_mcount_nc>
> 14: e3a00022 mov r0, #34 @ 0x22 ;; Hmmm...
> sizeof(xxx) changed?
> 18: e89da800 ldm sp, {fp, sp, pc}
Well for one -mabi=apcs-gnu and -mabi=aapcs-linux are 2 different ABIs
and have different rules.
The difference is due to the anonymous union:
> union { struct { unsigned short pn_15_0; unsigned int pn_47_16; }
> __attribute__((packed));
> struct { unsigned short pn_15_0; unsigned int pn_47_16; }
> __attribute__((packed)) pn;
> };
If we add __attribute__((packed)) at the end of the union, the size is
"corrected".
Since apcs-gnu is considered an ABI pre EABI for GCC I really doubt it
can be changed here.
Thanks,
Andrew
>
> Dmitry
