Record the address of a tail-calling branch instruction within its call
site entry using DW_AT_call_pc. This allows a debugger to determine the
address to use when creating aritificial frames.
This creates an extra attribute + relocation at tail call sites, which
constitute 3-5% of all call sites in xnu/clang respectively.
rdar://60307600
Differential Revision: https://reviews.llvm.org/D76336
A number of X86 tests were accidentally disabled in
https://reviews.llvm.org/D73568. This commit re-enables those tests.
```
$ for x86_test in $(gg 'REQUIRES: x86$' llvm/test | fst); do sed -i "" '/REQUIRES: x86/d' $x86_test; done
```
(Note that 'x86' is not an available feature, that's what caused the
tests to be disabled.)
Summary: The lit feature object-emission was added because Hexagon did not support the integrated assembler, so some tests needed to be turned off with a Hexagon target. Hexagon now supports the integrated assembler, so this feature can be removed.
Reviewers: bcain, kparzysz, jverma, whitequark, JDevlieghere
Reviewed By: JDevlieghere
Subscribers: mehdi_amini, hiraditya, steven_wu, dexonsmith, arphaman, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D73568
Currently, clang emits subprograms for declared functions when the
target debugger or DWARF standard is known to support entry values
(DW_OP_entry_value & the GNU equivalent).
Treat DW_AT_tail_call the same way to allow debuggers to follow cross-TU
tail calls.
Pre-patch debug session with a cross-TU tail call:
```
* frame #0: 0x0000000100000fa4 main`target at b.c:4:3 [opt]
frame #1: 0x0000000100000f99 main`main at a.c:8:10 [opt]
```
Post-patch (note that the tail-calling frame, "helper", is visible):
```
* frame #0: 0x0000000100000fa4 main`target at b.c:4:3 [opt]
frame #1: 0x0000000100000f80 main`helper [opt] [artificial]
frame #2: 0x0000000100000f99 main`main at a.c:8:10 [opt]
```
This was reverted in 5b9a072c because it attached declaration
subprograms to inlinable builtin calls, which interacted badly with the
MergeICmps pass. The fix is to not attach declarations to builtins.
rdar://46577651
Differential Revision: https://reviews.llvm.org/D69743
This caused Chromium builds to fail with "inlinable function call in a function
with debug info must have a !dbg location" errors. See
https://bugs.chromium.org/p/chromium/issues/detail?id=1022296#c1 for a
reproducer.
> Currently, clang emits subprograms for declared functions when the
> target debugger or DWARF standard is known to support entry values
> (DW_OP_entry_value & the GNU equivalent).
>
> Treat DW_AT_tail_call the same way to allow debuggers to follow cross-TU
> tail calls.
>
> Pre-patch debug session with a cross-TU tail call:
>
> ```
> * frame #0: 0x0000000100000fa4 main`target at b.c:4:3 [opt]
> frame #1: 0x0000000100000f99 main`main at a.c:8:10 [opt]
> ```
>
> Post-patch (note that the tail-calling frame, "helper", is visible):
>
> ```
> * frame #0: 0x0000000100000fa4 main`target at b.c:4:3 [opt]
> frame #1: 0x0000000100000f80 main`helper [opt] [artificial]
> frame #2: 0x0000000100000f99 main`main at a.c:8:10 [opt]
> ```
>
> rdar://46577651
>
> Differential Revision: https://reviews.llvm.org/D69743
Currently, clang emits subprograms for declared functions when the
target debugger or DWARF standard is known to support entry values
(DW_OP_entry_value & the GNU equivalent).
Treat DW_AT_tail_call the same way to allow debuggers to follow cross-TU
tail calls.
Pre-patch debug session with a cross-TU tail call:
```
* frame #0: 0x0000000100000fa4 main`target at b.c:4:3 [opt]
frame #1: 0x0000000100000f99 main`main at a.c:8:10 [opt]
```
Post-patch (note that the tail-calling frame, "helper", is visible):
```
* frame #0: 0x0000000100000fa4 main`target at b.c:4:3 [opt]
frame #1: 0x0000000100000f80 main`helper [opt] [artificial]
frame #2: 0x0000000100000f99 main`main at a.c:8:10 [opt]
```
rdar://46577651
Differential Revision: https://reviews.llvm.org/D69743
Dump the DWARF information about call sites and call site parameters into
debug info sections.
The patch also provides an interface for the interpretation of instructions
that could load values of a call site parameters in order to generate DWARF
about the call site parameters.
([13/13] Introduce the debug entry values.)
Co-authored-by: Ananth Sowda <asowda@cisco.com>
Co-authored-by: Nikola Prica <nikola.prica@rt-rk.com>
Co-authored-by: Ivan Baev <ibaev@cisco.com>
Differential Revision: https://reviews.llvm.org/D60716
llvm-svn: 365467
On the PPC bot, the %llc_dwarf substitution does not contain an -mtriple
argument. This can cause the wrong backend to be exercised.
This causes issues because the backends differ in when they decide to
emit tail calls:
http://lab.llvm.org:8011/builders/clang-ppc64be-linux-multistage/builds/12440
This is mostly a speculative fix as I don't have a PPC machine to test
with.
llvm-svn: 343893
DWARF v5 introduces DW_AT_call_all_calls, a subprogram attribute which
indicates that all calls (both regular and tail) within the subprogram
have call site entries. The information within these call site entries
can be used by a debugger to populate backtraces with synthetic tail
call frames.
Tail calling frames go missing in backtraces because the frame of the
caller is reused by the callee. Call site entries allow a debugger to
reconstruct a sequence of (tail) calls which led from one function to
another. This improves backtrace quality. There are limitations: tail
recursion isn't handled, variables within synthetic frames may not
survive to be inspected, etc. This approach is not novel, see:
https://gcc.gnu.org/wiki/summit2010?action=AttachFile&do=get&target=jelinek.pdf
This patch adds an IR-level flag (DIFlagAllCallsDescribed) which lowers
to DW_AT_call_all_calls. It adds the minimal amount of DWARF generation
support needed to emit standards-compliant call site entries. For easier
deployment, when the debugger tuning is LLDB, the DWARF requirement is
adjusted to v4.
Testing: Apart from check-{llvm, clang}, I built a stage2 RelWithDebInfo
clang binary. Its dSYM passed verification and grew by 1.4% compared to
the baseline. 151,879 call site entries were added.
rdar://42001377
Differential Revision: https://reviews.llvm.org/D49887
llvm-svn: 343883
Vedant Kumar