When the page_size < p_align of the ELF load segment, the loader
will end up creating extra PROT_NONE gap VMA mappings between the
LOAD segments. This problem is exacerbated by Android's zygote
model, where the number of loaded .so's can lead to ~30MB increase
in vm_area_struct unreclaimable slab memory.
Extend the LOAD segment VMA's to cover the range between the
segment's end and the start of the next segment, being careful
to avoid touching regions of the extended mapping where the offset
would overrun the size of the file. This avoids the loader
creating an additional gap VMA for each LOAD segment.
Consider a system with 4KB page size and the ELF files with 64K
alignment. e.g:
$ readelf -Wl /system/lib64/bootstrap/libc.so | grep 'Type\|LOAD'
Type Offset VirtAddr PhysAddr FileSiz MemSiz Flg Align
LOAD 0x000000 0x0000000000000000 0x0000000000000000 0x0441a8 0x0441a8 R 0x10000
LOAD 0x0441b0 0x00000000000541b0 0x00000000000541b0 0x091860 0x091860 R E 0x10000
LOAD 0x0d5a10 0x00000000000f5a10 0x00000000000f5a10 0x003d40 0x003d40 RW 0x10000
LOAD 0x0d9760 0x0000000000109760 0x0000000000109760 0x0005c0 0x459844 RW 0x10000
Before this patch:
$ cat /proc/1/maps | grep -A1 libc.so
7fa1d4a90000-7fa1d4ad5000 r--p 00000000 fe:09 20635520 /system/lib64/bootstrap/libc.so
7fa1d4ad5000-7fa1d4ae4000 ---p 00000000 00:00 0
7fa1d4ae4000-7fa1d4b76000 r-xp 00044000 fe:09 20635520 /system/lib64/bootstrap/libc.so
7fa1d4b76000-7fa1d4b85000 ---p 00000000 00:00 0
7fa1d4b85000-7fa1d4b8a000 r--p 000d5000 fe:09 20635520 /system/lib64/bootstrap/libc.so
7fa1d4b8a000-7fa1d4b99000 ---p 00000000 00:00 0
7fa1d4b99000-7fa1d4b9a000 rw-p 000d9000 fe:09 20635520 /system/lib64/bootstrap/libc.so
7fa1d4b9a000-7fa1d4feb000 rw-p 00000000 00:00 0 [anon:.bss]
3 additional PROT_NONE (---p) VMAs for gap mappings.
After this patch:
$ cat /proc/1/maps | grep -A1 libc.so
7f468f069000-7f468f0bd000 r--p 00000000 fe:09 20635520 /system/lib64/bootstrap/libc.so
7f468f0bd000-7f468f15e000 r-xp 00044000 fe:09 20635520 /system/lib64/bootstrap/libc.so
7f468f15e000-7f468f163000 r--p 000d5000 fe:09 20635520 /system/lib64/bootstrap/libc.so
7f468f163000-7f468f172000 rw-p 000da000 fe:09 20635520 /system/lib64/bootstrap/libc.so
7f468f172000-7f468f173000 rw-p 000d9000 fe:09 20635520 /system/lib64/bootstrap/libc.so
7f468f173000-7f468f5c4000 rw-p 00000000 00:00 0 [anon:.bss]
No additional gap VMAs. However notice there is an extra RW VMA at
offset 0x000da000. This is caused by the RO protection of the
GNU_RELRO segment, which causes the extended RW VMA to split.
The GNU_RELRO protection extension is handled in the subsequent
patch in this series.
Bug: 316403210
Bug: 300367402
Bug: 307803052
Bug: 312550202
Test: atest -c linker-unit-tests
Test: atest -c bionic-unit-tests
Change-Id: I7150ed22af0723cc0b2d326c046e4e4a8b56ad09
Signed-off-by: Kalesh Singh <kaleshsingh@google.com>
944164c5e2