tree d95f95609f40cb3bbf4d4b2693c7daf5fd15e79e
parent 2a6ee260cd30932ba84de8e8a4aa40131f694ec7
author Fangrui Song <maskray@google.com> 1569382771 +0000
committer Fangrui Song <maskray@google.com> 1569382771 +0000

[ELF] Add -z separate-loadable-segments to complement separate-code and noseparate-code

D64906 allows PT_LOAD to have overlapping p_offset ranges. In the
default R RX RW RW layout + -z noseparate-code case, we do not tail pad
segments when transiting to another segment. This can save at most
3*maxPageSize bytes.

a) Before D64906, we tail pad R, RX and the first RW.
b) With -z separate-code, we tail pad R and RX, but not the first RW (RELRO).

In some cases, b) saves one file page. In some cases, b) wastes one
virtual memory page. The waste is a concern on Fuchsia. Because it uses
compressed binaries, it doesn't benefit from the saved file page.

This patch adds -z separate-loadable-segments to restore the behavior before
D64906. It can affect section addresses and can thus be used as a
debugging mechanism (see PR43214 and ld.so partition bug in
crbug.com/998712).

Reviewed By: jakehehrlich, ruiu

Differential Revision: https://reviews.llvm.org/D67481

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@372807 91177308-0d34-0410-b5e6-96231b3b80d8