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Author	SHA1	Message	Date
Igor Kudrin	657e067bb5	[ARMInstPrinter] Print the target address of a branch instruction This follows other patches that changed printing immediate values of branch instructions to target addresses, see D76580 (x86), D76591 (PPC), D77853 (AArch64). As observing immediate values might sometimes be useful, they are printed as comments for branch instructions. // llvm-objdump -d output (before) 000200b4 <_start>: 200b4: ff ff ff fa blx #-4 <thumb> 000200b8 <thumb>: 200b8: ff f7 fc ef blx #-8 <_start> // llvm-objdump -d output (after) 000200b4 <_start>: 200b4: ff ff ff fa blx 0x200b8 <thumb> @ imm = #-4 000200b8 <thumb>: 200b8: ff f7 fc ef blx 0x200b4 <_start> @ imm = #-8 // GNU objdump -d. 000200b4 <_start>: 200b4: faffffff blx 200b8 <thumb> 000200b8 <thumb>: 200b8: f7ff effc blx 200b4 <_start> Differential Revision: https://reviews.llvm.org/D104701	2021-06-30 16:35:28 +07:00
Peter Smith	e35929e026	[LLD][ELF][ARM] Refactor inBranchRange to use addend for PC Bias In AArch32 ARM, the PC reads two instructions ahead of the currently executiing instruction. This evaluates to 8 in ARM state and 4 in Thumb state. Branch instructions on AArch32 compensate for this by subtracting the PC bias from the addend. For a branch to symbol this will result in an addend of -8 in ARM state and -4 in Thumb state. The existing ARM Target::inBranchRange function accounted for this implict addend within the function meaning that if the addend were to be taken into account by the caller then it would be double counted. This complicates the interface for all Targets as callers wanting to account for addends had to account for the ARM PC-bias. In certain situations such as: https://github.com/ClangBuiltLinux/linux/issues/1305 the PC-bias compensation code didn't match up. In particular normalizeExistingThunk() didn't put the PC-bias back in as Arm thunks did not store the addend. The simplest fix for the problem is to add the PC bias in normalizeExistingThunk when restoring the addend. However I think it is worth refactoring the Arm inBranchRange implementation so that fewer calls to getPCBias are needed for other Targets. I wasn't able to remove getPCBias completely but hopefully the Relocations.cpp code is simpler now. In principle a test could be written to replicate the linux kernel build failure but I wasn't able to reproduce with a small example that I could build up from scratch. Fixes https://github.com/ClangBuiltLinux/linux/issues/1305 Differential Revision: https://reviews.llvm.org/D97550	2021-03-02 11:02:33 +00:00

Author

SHA1

Message

Date

Igor Kudrin

657e067bb5

[ARMInstPrinter] Print the target address of a branch instruction

This follows other patches that changed printing immediate values of
branch instructions to target addresses, see D76580 (x86), D76591 (PPC),
D77853 (AArch64).

As observing immediate values might sometimes be useful, they are
printed as comments for branch instructions.

// llvm-objdump -d output (before)
000200b4 <_start>:
   200b4: ff ff ff fa   blx     #-4 <thumb>
000200b8 <thumb>:
   200b8: ff f7 fc ef   blx     #-8 <_start>

// llvm-objdump -d output (after)
000200b4 <_start>:
   200b4: ff ff ff fa   blx     0x200b8 <thumb>         @ imm = #-4
000200b8 <thumb>:
   200b8: ff f7 fc ef   blx     0x200b4 <_start>        @ imm = #-8

// GNU objdump -d.
000200b4 <_start>:
   200b4:       faffffff        blx     200b8 <thumb>
000200b8 <thumb>:
   200b8:       f7ff effc       blx     200b4 <_start>

Differential Revision: https://reviews.llvm.org/D104701

2021-06-30 16:35:28 +07:00

Peter Smith

e35929e026

[LLD][ELF][ARM] Refactor inBranchRange to use addend for PC Bias

In AArch32 ARM, the PC reads two instructions ahead of the currently
executiing instruction. This evaluates to 8 in ARM state and 4 in
Thumb state. Branch instructions on AArch32 compensate for this by
subtracting the PC bias from the addend. For a branch to symbol this
will result in an addend of -8 in ARM state and -4 in Thumb state.

The existing ARM Target::inBranchRange function accounted for this
implict addend within the function meaning that if the addend were
to be taken into account by the caller then it would be double
counted. This complicates the interface for all Targets as callers
wanting to account for addends had to account for the ARM PC-bias.

In certain situations such as:
https://github.com/ClangBuiltLinux/linux/issues/1305
the PC-bias compensation code didn't match up. In particular
normalizeExistingThunk() didn't put the PC-bias back in as Arm
thunks did not store the addend.

The simplest fix for the problem is to add the PC bias in
normalizeExistingThunk when restoring the addend. However I think
it is worth refactoring the Arm inBranchRange implementation so
that fewer calls to getPCBias are needed for other Targets. I
wasn't able to remove getPCBias completely but hopefully the
Relocations.cpp code is simpler now.

In principle a test could be written to replicate the linux kernel
build failure but I wasn't able to reproduce with a small example
that I could build up from scratch.

Fixes https://github.com/ClangBuiltLinux/linux/issues/1305

Differential Revision: https://reviews.llvm.org/D97550

2021-03-02 11:02:33 +00:00

2 Commits