From 676799a00d12db306ad592dd8962faa22d108bb9 Mon Sep 17 00:00:00 2001 From: Andriy Gapon Date: Fri, 23 Jul 2010 17:07:51 +0000 Subject: [PATCH] completely ignore zero-sized elf sections in modules of elf object type (amd64) Current code doesn't check size of elf sections and may perform needless actions of zero-sized memory allocation and similar. The bigger issue is that alignment requirement of a zero-sized section gets effectively applied to the next section if it has smaller alignment requirement. But other tools, like gdb and consequently kgdb, completely ignore zero-sized sections and thus may map symbols to addresses differently. Zero-sized sections are not typical in general. Their typical (only, even) cause in FreeBSD modules is inline assembly that creates custom sections which is found in pcpu.h and vnet.h. Mere inclusion of one of those header files produces a custom section in elf output. If there is no actual use for the section in a given module, then the section remains empty. Better solution is to avoid creating zero-sized sections altogether, which is in plans. Preloaded modules are handled in boot code (load_elf_obj.c), while dynamically loaded modules are handled by kernel (link_elf_obj.c). Based on code by: np MFC after: 3 weeks --- sys/boot/common/load_elf_obj.c | 2 ++ sys/kern/link_elf_obj.c | 6 ++++++ 2 files changed, 8 insertions(+) diff --git a/sys/boot/common/load_elf_obj.c b/sys/boot/common/load_elf_obj.c index 4b3aaeae786..6f3b3493aa3 100644 --- a/sys/boot/common/load_elf_obj.c +++ b/sys/boot/common/load_elf_obj.c @@ -221,6 +221,8 @@ __elfN(obj_loadimage)(struct preloaded_file *fp, elf_file_t ef, u_int64_t off) for (i = 0; i < hdr->e_shnum; i++) shdr[i].sh_addr = 0; for (i = 0; i < hdr->e_shnum; i++) { + if (shdr[i].sh_size == 0) + continue; switch (shdr[i].sh_type) { case SHT_PROGBITS: case SHT_NOBITS: diff --git a/sys/kern/link_elf_obj.c b/sys/kern/link_elf_obj.c index a337fd00c62..b0df57dcbac 100644 --- a/sys/kern/link_elf_obj.c +++ b/sys/kern/link_elf_obj.c @@ -555,6 +555,8 @@ link_elf_load_file(linker_class_t cls, const char *filename, symtabindex = -1; symstrindex = -1; for (i = 0; i < hdr->e_shnum; i++) { + if (shdr[i].sh_size == 0) + continue; switch (shdr[i].sh_type) { case SHT_PROGBITS: case SHT_NOBITS: @@ -677,6 +679,8 @@ link_elf_load_file(linker_class_t cls, const char *filename, /* Size up code/data(progbits) and bss(nobits). */ alignmask = 0; for (i = 0; i < hdr->e_shnum; i++) { + if (shdr[i].sh_size == 0) + continue; switch (shdr[i].sh_type) { case SHT_PROGBITS: case SHT_NOBITS: @@ -737,6 +741,8 @@ link_elf_load_file(linker_class_t cls, const char *filename, ra = 0; alignmask = 0; for (i = 0; i < hdr->e_shnum; i++) { + if (shdr[i].sh_size == 0) + continue; switch (shdr[i].sh_type) { case SHT_PROGBITS: case SHT_NOBITS: