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authorFlorian Weimer <fweimer@redhat.com>2022-01-17 09:57:19 +0100
committerFlorian Weimer <fweimer@redhat.com>2022-01-17 09:58:27 +0100
commit8eb2510d38226ce10a3a15109be948f052585106 (patch)
tree8881c230da9374d0ce76260a6b3ae44ba87a2940 /elf
parentb4d4ff8963866367ba861681ef3b1251e122014a (diff)
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elf: Set l_contiguous to 1 for the main map in more cases
l_contiguous was not initialized at all for the main map and always 0. This commit adds code to check if the LOAD segments are adjacent to each other, and sets l_contiguous accordingly. This helps _dl_find_object because it is more efficient if the main mapping is contiguous. Note that not all (PIE or non-PIE) binaries are contiguous in this way because BFD ld creates executables with LOAD holes: ELF LOAD segments creating holes in the process image on GNU/Linux https://sourceware.org/pipermail/binutils/2022-January/119082.html https://sourceware.org/bugzilla/show_bug.cgi?id=28743 Reviewed-by: H.J. Lu <hjl.tools@gmail.com>
Diffstat (limited to 'elf')
-rw-r--r--elf/rtld.c25
1 files changed, 25 insertions, 0 deletions
diff --git a/elf/rtld.c b/elf/rtld.c
index 4e0581e..8d233f7 100644
--- a/elf/rtld.c
+++ b/elf/rtld.c
@@ -1147,6 +1147,22 @@ rtld_setup_main_map (struct link_map *main_map)
main_map->l_map_start = ~0;
/* And it was opened directly. */
++main_map->l_direct_opencount;
+ main_map->l_contiguous = 1;
+
+ /* A PT_LOAD segment at an unexpected address will clear the
+ l_contiguous flag. The ELF specification says that PT_LOAD
+ segments need to be sorted in in increasing order, but perhaps
+ not all executables follow this requirement. Having l_contiguous
+ equal to 1 is just an optimization, so the code below does not
+ try to sort the segments in case they are unordered.
+
+ There is one corner case in which l_contiguous is not set to 1,
+ but where it could be set: If a PIE (ET_DYN) binary is loaded by
+ glibc itself (not the kernel), it is always contiguous due to the
+ way the glibc loader works. However, the kernel loader may still
+ create holes in this case, and the code here still uses 0
+ conservatively for the glibc-loaded case, too. */
+ ElfW(Addr) expected_load_address = 0;
/* Scan the program header table for the dynamic section. */
for (const ElfW(Phdr) *ph = phdr; ph < &phdr[phnum]; ++ph)
@@ -1210,12 +1226,21 @@ rtld_setup_main_map (struct link_map *main_map)
if (main_map->l_map_start > mapstart)
main_map->l_map_start = mapstart;
+ if (main_map->l_contiguous && expected_load_address != 0
+ && expected_load_address != mapstart)
+ main_map->l_contiguous = 0;
+
/* Also where it ends. */
allocend = main_map->l_addr + ph->p_vaddr + ph->p_memsz;
if (main_map->l_map_end < allocend)
main_map->l_map_end = allocend;
if ((ph->p_flags & PF_X) && allocend > main_map->l_text_end)
main_map->l_text_end = allocend;
+
+ /* The next expected address is the page following this load
+ segment. */
+ expected_load_address = ((allocend + GLRO(dl_pagesize) - 1)
+ & ~(GLRO(dl_pagesize) - 1));
}
break;