Cp/r139712783 correct fix to retrieve link register above fault handler #9645
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llvm#92503) …unction (llvm#91321)" This reapplies fd1bd53, which was reverted due to a test failure on aarch64/windows. The failure was caused by a combination of several factors: - clang targeting aarch64-windows (unlike msvc, and unlike clang targeting other aarch64 platforms) defaults to -fomit-frame-pointers - lldb's code for looking up register values for `<same>` unwind rules is recursive - the test binary creates a very long chain of fp-less function frames (it manages to fit about 22k frames before it blows its stack) Together, these things have caused lldb to recreate the same deep recursion when unwinding through this, and blow its own stack as well. Since lldb frames are larger, about 4k frames like this was sufficient to trigger the stack overflow. This version of the patch works around this problem by increasing the frame size of the test binary, thereby causing it to blow its stack sooner. This doesn't fix the issue -- the same problem can occur with a real binary -- but it's not very likely, as it requires an infinite recursion in a simple (so it doesn't use the frame pointer) function with a very small frame (so you can fit a lot of them on the stack). A more principled fix would be to make lldb's lookup code non-recursive, but I believe that's out of scope for this patch. The original patch description follows: A leaf function may not store the link register to stack, but we it can still end up being a non-zero frame if it gets interrupted by a signal. Currently, we were unable to unwind past this function because we could not read the link register value. To make this work, this patch: - changes the function-entry unwind plan to include the `fp|lr = <same>` rules. This in turn necessitated an adjustment in the generic instruction emulation logic to ensure that `lr=[sp-X]` can override the `<same>` rule. - allows the `<same>` rule for pc and lr in all `m_all_registers_available` frames (and not just frame zero). The test verifies that we can unwind in a situation like this, and that the backtrace matches the one we computed before getting a signal. (cherry picked from commit bbd54e0)
…llvm#98566)" This reverts commit fd42417. This patch has two problems. First, it is unnecessary, Pavel landed a fix a week or so before mine which solves this problem in bbd54e0 . Second, the fix is incorrect; for a function above a trap handler, where all registers are available, this patch would have lldb fetch the return address register from frame 0. This might be 10 frames up in the stack; the frame 0 return address register is incorrect. The change would have been correct a short bit later than this, but Pavel's fix is executed earlier in the function and none of this is needed. (cherry picked from commit d29a50f)
JDevlieghere
approved these changes
Nov 20, 2024
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