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Only perform .bss mapping and cleaning operations when segment file size

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is not equal to its memory size.

This eliminates unneeded clearing of the text segment that often
happens due to text end not being page-aligned.

For instance,
$ readelf -l /lib/libedit.so.6
Program Headers:
  Type           Offset   VirtAddr   PhysAddr   FileSiz MemSiz  Flg Align
  LOAD           0x000000 0x00000000 0x00000000 0x139e1 0x139e1 R E 0x1000
  LOAD           0x014000 0x00014000 0x00014000 0x00f04 0x00f14 RW  0x1000
  DYNAMIC        0x014cc4 0x00014cc4 0x00014cc4 0x000d0 0x000d0 RW  0x4
$ procstat -v $$ (for /bin/sh)
68585 0x28097000 0x280aa000 r-x    6    0  21  14 CN vn /lib/libedit.so.6
68585 0x280aa000 0x280ab000 r-x    1    0   1   0 CN vn /lib/libedit.so.6 <==
68585 0x280ab000 0x280ac000 rwx    1    0   1   0 CN vn /lib/libedit.so.6
Note the splitted map entry marked by '<=='.

Reviewed by:	kan
Approved by:	re (kensmith)
MFC after:	1 month
This commit is contained in:
Konstantin Belousov 2009-07-17 19:32:04 +00:00
parent 8b9fde4324
commit 69ca61ba5e
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=195743
1 changed files with 28 additions and 22 deletions
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50
libexec/rtld-elf/map_object.c
View File

@ -180,37 +180,43 @@ map_object(int fd, const char *path, const struct stat *sb)
return NULL;
}
/* Clear any BSS in the last page of the segment. */
clear_vaddr = segs[i]->p_vaddr + segs[i]->p_filesz;
clear_addr = mapbase + (clear_vaddr - base_vaddr);
clear_page = mapbase + (trunc_page(clear_vaddr) - base_vaddr);
if ((nclear = data_vlimit - clear_vaddr) > 0) {
/* Make sure the end of the segment is writable */
if ((data_prot & PROT_WRITE) == 0 &&
-1 == mprotect(clear_page, PAGE_SIZE, data_prot|PROT_WRITE)) {
/* Do BSS setup */
if (segs[i]->p_filesz != segs[i]->p_memsz) {
/* Clear any BSS in the last page of the segment. */
clear_vaddr = segs[i]->p_vaddr + segs[i]->p_filesz;
clear_addr = mapbase + (clear_vaddr - base_vaddr);
clear_page = mapbase + (trunc_page(clear_vaddr) - base_vaddr);
if ((nclear = data_vlimit - clear_vaddr) > 0) {
/* Make sure the end of the segment is writable */
if ((data_prot & PROT_WRITE) == 0 && -1 ==
mprotect(clear_page, PAGE_SIZE, data_prot|PROT_WRITE)) {
_rtld_error("%s: mprotect failed: %s", path,
strerror(errno));
return NULL;
}
memset(clear_addr, 0, nclear);
/* Reset the data protection back */
if ((data_prot & PROT_WRITE) == 0)
mprotect(clear_page, PAGE_SIZE, data_prot);
}
memset(clear_addr, 0, nclear);
/* Reset the data protection back */
if ((data_prot & PROT_WRITE) == 0)
mprotect(clear_page, PAGE_SIZE, data_prot);
}
/* Overlay the BSS segment onto the proper region. */
bss_vaddr = data_vlimit;
bss_vlimit = round_page(segs[i]->p_vaddr + segs[i]->p_memsz);
bss_addr = mapbase + (bss_vaddr - base_vaddr);
if (bss_vlimit > bss_vaddr) { /* There is something to do */
if (mprotect(bss_addr, bss_vlimit - bss_vaddr, data_prot) == -1) {
/* Overlay the BSS segment onto the proper region. */
bss_vaddr = data_vlimit;
bss_vlimit = round_page(segs[i]->p_vaddr + segs[i]->p_memsz);
bss_addr = mapbase + (bss_vaddr - base_vaddr);
if (bss_vlimit > bss_vaddr) { /* There is something to do */
if (mprotect(bss_addr, bss_vlimit - bss_vaddr, data_prot) == -1) {
_rtld_error("%s: mprotect of bss failed: %s", path,
strerror(errno));
return NULL;
return NULL;
}
}
}
if (phdr_vaddr == 0 && data_offset <= hdr->e_phoff &&
(data_vlimit - data_vaddr + data_offset) >=
(hdr->e_phoff + hdr->e_phnum * sizeof (Elf_Phdr))) {