objtool: Support multiple rodata sections.

This commit adds support for processing switch jump tables in objects
with multiple .rodata sections, such as those created when using
-ffunction-sections and -fdata-sections.  Currently, objtool always
looks in .rodata for jump table information which results in many
"sibling call from callable instruction with modified stack frame"
warnings with objects compiled using those flags.

The fix is comprised of three parts:

1. Flagging all .rodata sections when importing elf information for
easier checking later.

2. Keeping a reference to the section each relocation is from in order
to get the list_head for the other relocations in that section.

3. Finding jump tables by following relocations to .rodata sections,
rather than always referencing a single global .rodata section.

The patch has been tested without data sections enabled and no
differences in the resulting orc unwind information were seen.

Note that as objtool adds terminators to end of each .text section the
unwind information generated between a function+data sections build and
a normal build aren't directly comparable. Manual inspection suggests
that objtool is now generating the correct information, or at least
making more of an effort to do so than it did previously.

Signed-off-by: Allan Xavier <allan.x.xavier@oracle.com>
4 files changed