|
|
EDA365欢迎您登录！
您需要 登录 才可以下载或查看，没有帐号？注册
x
% e4 _8 z5 K& x* [! F
linux 内核庞大而复杂。内核代码阅读的时候，有没有遇到因为宏定义或者inline层次太深而不知道到底代码是什么样子。代码预处理可以解决这个难题。
6 t; {, x/ f& D. L+ p% k8 l& b: ~4 F0 ~) S s- {
平台：linux 3.4.5 ARM，PC linux上类似，更简单些。
& ^, w+ g9 @& Z: j0 e2 O$ Y, \' p: b6 m
加V=1重新编译内核/ F ?5 C( t4 T8 {- K* X. T
6 p1 m- @4 K! `+ K& U
make内核增加V=1选项，会详细打印编译过程，-B是要求重新编译内核所有模块。; ?8 H* D+ [6 D' l0 J: N; ?
2 l: J' B4 `% _+ A- cd linux-3.4.5 && make ARCH=arm defconfig && make ARCH=arm CROSS_COMPILE=arm-buildroot-linux-uclibcgnueabi- EXTRAVERSION=- -B V=1 uImage0 X: W, w8 r) x9 p3 r8 x' O/ k
- K$ T: |9 ^+ y/ E' `: W' Q编译内核并保存编译log到文件，搜索你要预编译的文件，如mm/slab.c，会找到如下编译命令：: c8 D1 \. g% X. u0 j" V" `
# i4 b3 k8 d' A- k0 g- arm-buildroot-linux-uclibcgnueabi-gcc -Wp,-MD,mm/.slab.o.d -nostdinc -isystem /home/test/build/gcc-4.9.8/build_arm/staging_dir/usr/bin/../lib/gcc/arm-buildroot-linux-uclibcgnueabi/4.9.8/include -I/home/test/linux/kernels/linux-3.4.5/arch/arm/include -Iarch/arm/include/generated -Iinclude -include /home/test/linux/kernels/linux-3.4.5/include/linux/kconfig.h -D__KERNEL__ -mlittle-endian -Iarch/arm/mach-zx297510/include -Wall -Wundef -Wstrict-prototypes -Wno-trigraphs -fno-strict-aliasing -fno-common -Werror-implicit-function-declaration -Wno-format-security -fno-delete-null-pointer-checks -O2 -marm -fno-dwaRF2-cfi-asm -mabi=aapcs-linux -mno-thumb-interwork -funwind-tables -D__LINUX_ARM_ARCH__=7 -march=armv7-a -msoft-float -Uarm -Wframe-larger-than=1024 -fno-stack-protector -Wno-unused-but-set-variable -fomit-frame-pointer -g -fno-inline-functions-called-once -Wdeclaration-after-statement -Wno-pointer-sign -fno-strict-overflow -fconserve-stack -DCC_HAVE_ASM_GOTO -D"KBUILD_STR(s)=#s" -D"KBUILD_BASENAME=KBUILD_STR(slab)" -D"KBUILD_MODNAME=KBUILD_STR(slab)" -c -o mm/.tmp_slab.o mm/slab.c
+ u0 m2 u1 e$ r% W6 G) D) C/ Y
. K+ ?. R" c ~7 Z编译预处理指定文件( k* I: r$ C" |8 O" h; W# e
4 G) O' Z; a$ q8 Z0 U$ D' |! c把编译命令修改成预处理命令：-c -o mm/.tmp_slab.o修改成-E -o mm/slab.E mm/slab.c，在内核目录linux-3.4.5直接执行。如果是交叉编译链，可能需要把arm-buildroot-linux-uclibcgnueabi-gcc所在路径加入到环境变量PATH里。
& S! z0 O5 A& o( }8 @3 Z
( d# j: W+ Y0 T1 H- arm-buildroot-linux-uclibcgnueabi-gcc -Wp,-MD,mm/.slab.o.d -nostdinc -isystem /home/test/build/gcc-4.9.8/build_arm/staging_dir/usr/bin/../lib/gcc/arm-buildroot-linux-uclibcgnueabi/4.9.8/include -I/home/test/linux/kernels/linux-3.4.5/arch/arm/include -Iarch/arm/include/generated -Iinclude -include /home/test/linux/kernels/linux-3.4.5/include/linux/kconfig.h -D__KERNEL__ -mlittle-endian -Iarch/arm/mach-zx297510/include -Wall -Wundef -Wstrict-prototypes -Wno-trigraphs -fno-strict-aliasing -fno-common -Werror-implicit-function-declaration -Wno-format-security -fno-delete-null-pointer-checks -O2 -marm -fno-dwarf2-cfi-asm -mabi=aapcs-linux -mno-thumb-interwork -funwind-tables -D__LINUX_ARM_ARCH__=7 -march=armv7-a -msoft-float -Uarm -Wframe-larger-than=1024 -fno-stack-protector -Wno-unused-but-set-variable -fomit-frame-pointer -g -fno-inline-functions-called-once -Wdeclaration-after-statement -Wno-pointer-sign -fno-strict-overflow -fconserve-stack -DCC_HAVE_ASM_GOTO -D"KBUILD_STR(s)=#s" -D"KBUILD_BASENAME=KBUILD_STR(slab)" -D"KBUILD_MODNAME=KBUILD_STR(slab)" -E -o mm/slab.E mm/slab.c
5 V0 K3 O( T, r* {
0 ` Z. t2 Z6 W4 t+ ^执行完命令，在内核的mm目录就能看到slab.c的预处理后文件slab.E文件了。看一下kmalloc函数代码，是不是清晰很多了。1 B/ C& T6 W6 C) z. D% \
$ C& a* s R, ?7 L4 v3 q4 }! Z8 ?, b
slab_def.h里的原始kmalloc
/ g: H, ~/ p7 W* P3 ~2 d4 _0 l9 c2 `- w8 s
- static __always_inline void *kmalloc(size_t size, gfp_t flags)
- {
- struct kmem_cache *cachep;
- void *ret;
- if (__builtin_constant_p(size)) {
- int i = 0;
- if (!size)
- return ZERO_SIZE_PTR;
- #define CACHE(x) \
- if (size <= x) \
- goto found; \
- else \
- i++;
- #include <linux/kmalloc_sizes.h>
- #undef CACHE
- return NULL;
- found:
- #ifdef CONFIG_ZONE_DMA
- if (flags & GFP_DMA)
- cachep = malloc_sizes.cs_dmacachep;
- else
- #endif
- cachep = malloc_sizes.cs_cachep;
- ret = kmem_cache_alloc_trace(size, cachep, flags);
- return ret;
- }
- return __kmalloc(size, flags);
- }$ u9 u8 T' D7 n3 }3 }% E
! X5 g6 b* |8 m: X, O预处理后的kmalloc,流程是不是清晰多了。
# O ^9 j/ }0 p8 P! r7 k+ Y+ \2 k- q& u4 ~7 _8 @5 m; G
- static inline __attribute__((always_inline)) __attribute__((always_inline)) void *kmalloc(size_t size, gfp_t flags)
- {
- struct kmem_cache *cachep;
- void *ret;
- if (__builtin_constant_p(size)) {
- int i = 0;
- if (!size)
- return ((void *)16);
- # 1 "include/linux/kmalloc_sizes.h" 1
- if (size <= 32) goto found; else i++;
- if (size <= 64) goto found; else i++;
- if (size <= 128) goto found; else i++;
- if (size <= 192) goto found; else i++;
- if (size <= 256) goto found; else i++;
- if (size <= 512) goto found; else i++;
- if (size <= 1024) goto found; else i++;
- if (size <= 2048) goto found; else i++;
- if (size <= 4096) goto found; else i++;
- if (size <= 8192) goto found; else i++;
- if (size <= 16384) goto found; else i++;
- if (size <= 32768) goto found; else i++;
- if (size <= 65536) goto found; else i++;
- if (size <= 131072) goto found; else i++;
- if (size <= 262144) goto found; else i++;
- if (size <= 524288) goto found; else i++;
- if (size <= 1048576) goto found; else i++;
- if (size <= 2097152) goto found; else i++;
- if (size <= 4194304) goto found; else i++;
- # 145 "include/linux/slab_def.h" 2
- return ((void *)0);
- found:
- cachep = malloc_sizes.cs_cachep;
- ret = kmem_cache_alloc_trace(size, cachep, flags);
- return ret;
- }
- return __kmalloc(size, flags);
- }
: q" s% w7 Y. x% @8 {
|
|
/1 
发表于 2020-2-6 09:47
收藏
淘帖
支持！
反对！