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Fix externalization on Userpsace Livepatching #124

Merged
merged 3 commits into from
Aug 23, 2024
Merged

Fix externalization on Userpsace Livepatching #124

merged 3 commits into from
Aug 23, 2024

Commits on Aug 22, 2024

  1. Disable const propagation on externalized vars 

    The value of the externalized vars are filled by the livepatch system,
not the compiler.  Hence if there are no writes into the variable
the compiler won't generate the instructions to read it.  As an
example:

```
static int aa;
int f(void) { return aa; }
```
generates:
```
  xor eax, eax
  ret
```
Notice how there is no memory read.  Adding the `__attribute__((used))`
to it changes the asm code to:
```
  movl	aa(%rip), %eax
  ret
```
Fixing the issue.

Signed-off-by: Giuliano Belinassi <[email protected]>
    @giulianobelinassi
    giulianobelinassi committed Aug 22, 2024
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  2. Fix symbol visibility 

    In the case the symbol is only available on SYMTAB we can't weakly
externalize it, as the linker will resolve it as not found.

Signed-off-by: Giuliano Belinassi <[email protected]>
    @giulianobelinassi
    giulianobelinassi committed Aug 22, 2024
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  3. Add option to pass two debuginfos 

    SUSE packages contain the stripped .so file with .dynsym and the
debuginfo (.debug) provided in -debuginfo packages.  We need both
of them in Userspace Livepatching since 15.5 for proper analysis.
This commit patches the ElfCache and InlineAnalysis so it can use
both of them.

For kernel we expect it to only use one ELF file for now (the
first one).

Signed-off-by: Giuliano Belinassi <[email protected]>
    @giulianobelinassi
    giulianobelinassi committed Aug 22, 2024
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