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| author | Daniel Dunbar <daniel@zuster.org> | 2010-03-23 02:36:58 +0000 |
|---|---|---|
| committer | Daniel Dunbar <daniel@zuster.org> | 2010-03-23 02:36:58 +0000 |
| commit | 8f9b80e5df12779a56d763ebf20864dad2bc72da (patch) | |
| tree | a1843332964b99c6d06bf5677c33203f9babd3c7 /lib/Target/X86/X86AsmBackend.cpp | |
| parent | 829680048cdfea7498587a03f815915f1c0e1965 (diff) | |
| download | external_llvm-8f9b80e5df12779a56d763ebf20864dad2bc72da.zip external_llvm-8f9b80e5df12779a56d763ebf20864dad2bc72da.tar.gz external_llvm-8f9b80e5df12779a56d763ebf20864dad2bc72da.tar.bz2 | |
MC: Add TargetAsmBackend::WriteNopData and use to eliminate some target dependencies in MCMachOStreamer and MCAssembler.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@99248 91177308-0d34-0410-b5e6-96231b3b80d8
Diffstat (limited to 'lib/Target/X86/X86AsmBackend.cpp')
| -rw-r--r-- | lib/Target/X86/X86AsmBackend.cpp | 63 |
1 files changed, 63 insertions, 0 deletions
diff --git a/lib/Target/X86/X86AsmBackend.cpp b/lib/Target/X86/X86AsmBackend.cpp index e918cb0..3e4e2b5 100644 --- a/lib/Target/X86/X86AsmBackend.cpp +++ b/lib/Target/X86/X86AsmBackend.cpp @@ -53,6 +53,8 @@ public: } void RelaxInstruction(const MCInstFragment *IF, MCInst &Res) const; + + bool WriteNopData(uint64_t Count, MCObjectWriter *OW) const; }; static unsigned getRelaxedOpcode(unsigned Op) { @@ -98,6 +100,67 @@ void X86AsmBackend::RelaxInstruction(const MCInstFragment *IF, Res.setOpcode(RelaxedOp); } +/// WriteNopData - Write optimal nops to the output file for the \arg Count +/// bytes. This returns the number of bytes written. It may return 0 if +/// the \arg Count is more than the maximum optimal nops. +/// +/// FIXME this is X86 32-bit specific and should move to a better place. +bool X86AsmBackend::WriteNopData(uint64_t Count, MCObjectWriter *OW) const { + static const uint8_t Nops[16][16] = { + // nop + {0x90}, + // xchg %ax,%ax + {0x66, 0x90}, + // nopl (%[re]ax) + {0x0f, 0x1f, 0x00}, + // nopl 0(%[re]ax) + {0x0f, 0x1f, 0x40, 0x00}, + // nopl 0(%[re]ax,%[re]ax,1) + {0x0f, 0x1f, 0x44, 0x00, 0x00}, + // nopw 0(%[re]ax,%[re]ax,1) + {0x66, 0x0f, 0x1f, 0x44, 0x00, 0x00}, + // nopl 0L(%[re]ax) + {0x0f, 0x1f, 0x80, 0x00, 0x00, 0x00, 0x00}, + // nopl 0L(%[re]ax,%[re]ax,1) + {0x0f, 0x1f, 0x84, 0x00, 0x00, 0x00, 0x00, 0x00}, + // nopw 0L(%[re]ax,%[re]ax,1) + {0x66, 0x0f, 0x1f, 0x84, 0x00, 0x00, 0x00, 0x00, 0x00}, + // nopw %cs:0L(%[re]ax,%[re]ax,1) + {0x66, 0x2e, 0x0f, 0x1f, 0x84, 0x00, 0x00, 0x00, 0x00, 0x00}, + // nopl 0(%[re]ax,%[re]ax,1) + // nopw 0(%[re]ax,%[re]ax,1) + {0x0f, 0x1f, 0x44, 0x00, 0x00, + 0x66, 0x0f, 0x1f, 0x44, 0x00, 0x00}, + // nopw 0(%[re]ax,%[re]ax,1) + // nopw 0(%[re]ax,%[re]ax,1) + {0x66, 0x0f, 0x1f, 0x44, 0x00, 0x00, + 0x66, 0x0f, 0x1f, 0x44, 0x00, 0x00}, + // nopw 0(%[re]ax,%[re]ax,1) + // nopl 0L(%[re]ax) */ + {0x66, 0x0f, 0x1f, 0x44, 0x00, 0x00, + 0x0f, 0x1f, 0x80, 0x00, 0x00, 0x00, 0x00}, + // nopl 0L(%[re]ax) + // nopl 0L(%[re]ax) + {0x0f, 0x1f, 0x80, 0x00, 0x00, 0x00, 0x00, + 0x0f, 0x1f, 0x80, 0x00, 0x00, 0x00, 0x00}, + // nopl 0L(%[re]ax) + // nopl 0L(%[re]ax,%[re]ax,1) + {0x0f, 0x1f, 0x80, 0x00, 0x00, 0x00, 0x00, + 0x0f, 0x1f, 0x84, 0x00, 0x00, 0x00, 0x00, 0x00} + }; + + // Write an optimal sequence for the first 15 bytes. + uint64_t OptimalCount = (Count < 16) ? Count : 15; + for (uint64_t i = 0, e = OptimalCount; i != e; i++) + OW->Write8(Nops[OptimalCount - 1][i]); + + // Finish with single byte nops. + for (uint64_t i = OptimalCount, e = Count; i != e; ++i) + OW->Write8(0x90); + + return true; +} + /* *** */ class ELFX86AsmBackend : public X86AsmBackend { |