https://sourceware.org/bugzilla/show_bug.cgi?id=18829
Bug ID: 18829
Summary: Add the ability to sort PLT entries
Product: binutils
Version: 2.26 (HEAD)
Status: NEW
Severity: enhancement
Priority: P2
Component: ld
Assignee: unassigned at sourceware dot org
Reporter: gregory.d.bentley at intel dot com
Target Milestone: ---
Created attachment 8524
--> https://sourceware.org/bugzilla/attachment.cgi?id=8524&action=edit
binutils patch to add -z sortplt
The jump instructions in the Procedure Linkage Table which effect the jump into
shared library functions are laid out in more or less random order. While one
can use a linker script to get more cache friendly layout of functions within
an executable, there is currently no way to explicitly specify the order of the
PLT entries. This means you can get into the situation where you have only 1
jump instruction (6 bytes) being "hot" on a 64 byte cache line.
The attached patch allows a user to specify a file which lists the names of hot
shared library functions. The PLT entries for those functions will be placed
into the table first, with any unspecified functions following.
The syntax is -z sortplt=<filename>
(As a side note, -z bndplt also gives more cache friendly code as it splits the
cold (first call) code from the hot (every call) code.)
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