[llvm] [BOLT] Add --custom-allocation-vma flag (PR #136385)
Rafael Auler via llvm-commits
llvm-commits at lists.llvm.org
Fri Apr 18 17:50:31 PDT 2025
https://github.com/rafaelauler updated https://github.com/llvm/llvm-project/pull/136385
>From 58ec6db18251fe76370af83504caf1802827afea Mon Sep 17 00:00:00 2001
From: Rafael Auler <rafaelauler at fb.com>
Date: Fri, 18 Apr 2025 15:03:48 -0700
Subject: [PATCH 1/2] [BOLT] Add --custom-allocation-vma flag
---
bolt/lib/Rewrite/RewriteInstance.cpp | 26 ++++++++++++++++
bolt/test/X86/high-segments.s | 46 ++++++++++++++++++++++++++++
2 files changed, 72 insertions(+)
create mode 100644 bolt/test/X86/high-segments.s
diff --git a/bolt/lib/Rewrite/RewriteInstance.cpp b/bolt/lib/Rewrite/RewriteInstance.cpp
index 45bc995ce906f..0c3daccaa6749 100644
--- a/bolt/lib/Rewrite/RewriteInstance.cpp
+++ b/bolt/lib/Rewrite/RewriteInstance.cpp
@@ -237,6 +237,13 @@ UseGnuStack("use-gnu-stack",
cl::ZeroOrMore,
cl::cat(BoltCategory));
+static cl::opt<uint64_t>
+CustomAllocationVMA("custom-allocation-vma",
+ cl::desc("use a custom address at which new code will be put, "
+ "bypassing BOLT's logic to detect where to put code"),
+ cl::ZeroOrMore,
+ cl::cat(BoltCategory));
+
static cl::opt<bool>
SequentialDisassembly("sequential-disassembly",
cl::desc("performs disassembly sequentially"),
@@ -592,6 +599,25 @@ Error RewriteInstance::discoverStorage() {
FirstNonAllocatableOffset = NextAvailableOffset;
+ if (opts::CustomAllocationVMA) {
+ // If user specified a custom address where we should start writing new
+ // data, honor that.
+ NextAvailableAddress = opts::CustomAllocationVMA;
+ // Sanity check the user-supplied address and emit warnings if something
+ // seems off.
+ for (const ELF64LE::Phdr &Phdr : PHs) {
+ switch (Phdr.p_type) {
+ case ELF::PT_LOAD:
+ if (NextAvailableAddress >= Phdr.p_vaddr &&
+ NextAvailableAddress < Phdr.p_vaddr + Phdr.p_memsz) {
+ BC->errs() << "BOLT-WARNING: user-supplied allocation vma 0x"
+ << Twine::utohexstr(NextAvailableAddress)
+ << " conflicts with ELF segment at 0x"
+ << Twine::utohexstr(Phdr.p_vaddr) << "\n";
+ }
+ }
+ }
+ }
NextAvailableAddress = alignTo(NextAvailableAddress, BC->PageAlign);
NextAvailableOffset = alignTo(NextAvailableOffset, BC->PageAlign);
diff --git a/bolt/test/X86/high-segments.s b/bolt/test/X86/high-segments.s
new file mode 100644
index 0000000000000..dfddf18004c2a
--- /dev/null
+++ b/bolt/test/X86/high-segments.s
@@ -0,0 +1,46 @@
+// Check that we are able to rewrite binaries when we fail to identify a
+// suitable location to put new code and user supplies a custom one via
+// --custom-allocation-vma. This happens more obviously if the binary has
+// segments mapped to very high addresses.
+
+// In this example, my.reserved.section is mapped to a segment to be loaded
+// at address 0x10000000000, while regular text should be at 0x200000. We
+// pick a vma in the middle at 0x700000 to carve space for BOLT to put data,
+// since BOLT's usual route of allocating after the last segment will put
+// code far away and that will blow up relocations from main.
+
+// RUN: split-file %s %t
+// RUN: llvm-mc -filetype=obj -triple x86_64-unknown-unknown %t/main.s -o %t.o
+// RUN: %clang %cflags -no-pie %t.o -o %t.exe -Wl,-T %t/main.ls
+// RUN: llvm-bolt %t.exe -o %t.bolt --custom-allocation-vma=0x700000
+
+//--- main.s
+ .type reserved_space, at object
+ .section .my.reserved.section,"awx", at nobits
+ .globl reserved_space
+ .p2align 4, 0x0
+reserved_space:
+ .zero 0x80000000
+ .size reserved_space, 0x80000000
+
+ .text
+ .globl main
+ .globl _start
+ .type main, %function
+_start:
+main:
+ .cfi_startproc
+ nop
+ nop
+ nop
+ retq
+ .cfi_endproc
+.size main, .-main
+
+//--- main.ls
+SECTIONS
+{
+ .my.reserved.section 1<<40 : {
+ *(.my.reserved.section);
+ }
+} INSERT BEFORE .comment;
>From 3c806af61e03f2678e4d83a258a5bba0875750c5 Mon Sep 17 00:00:00 2001
From: Rafael Auler <rafaelauler at fb.com>
Date: Fri, 18 Apr 2025 17:37:00 -0700
Subject: [PATCH 2/2] format
---
bolt/lib/Rewrite/RewriteInstance.cpp | 27 +++++++++++++--------------
1 file changed, 13 insertions(+), 14 deletions(-)
diff --git a/bolt/lib/Rewrite/RewriteInstance.cpp b/bolt/lib/Rewrite/RewriteInstance.cpp
index 0c3daccaa6749..718c90b04b282 100644
--- a/bolt/lib/Rewrite/RewriteInstance.cpp
+++ b/bolt/lib/Rewrite/RewriteInstance.cpp
@@ -237,12 +237,11 @@ UseGnuStack("use-gnu-stack",
cl::ZeroOrMore,
cl::cat(BoltCategory));
-static cl::opt<uint64_t>
-CustomAllocationVMA("custom-allocation-vma",
- cl::desc("use a custom address at which new code will be put, "
- "bypassing BOLT's logic to detect where to put code"),
- cl::ZeroOrMore,
- cl::cat(BoltCategory));
+static cl::opt<uint64_t> CustomAllocationVMA(
+ "custom-allocation-vma",
+ cl::desc("use a custom address at which new code will be put, "
+ "bypassing BOLT's logic to detect where to put code"),
+ cl::ZeroOrMore, cl::cat(BoltCategory));
static cl::opt<bool>
SequentialDisassembly("sequential-disassembly",
@@ -607,14 +606,14 @@ Error RewriteInstance::discoverStorage() {
// seems off.
for (const ELF64LE::Phdr &Phdr : PHs) {
switch (Phdr.p_type) {
- case ELF::PT_LOAD:
- if (NextAvailableAddress >= Phdr.p_vaddr &&
- NextAvailableAddress < Phdr.p_vaddr + Phdr.p_memsz) {
- BC->errs() << "BOLT-WARNING: user-supplied allocation vma 0x"
- << Twine::utohexstr(NextAvailableAddress)
- << " conflicts with ELF segment at 0x"
- << Twine::utohexstr(Phdr.p_vaddr) << "\n";
- }
+ case ELF::PT_LOAD:
+ if (NextAvailableAddress >= Phdr.p_vaddr &&
+ NextAvailableAddress < Phdr.p_vaddr + Phdr.p_memsz) {
+ BC->errs() << "BOLT-WARNING: user-supplied allocation vma 0x"
+ << Twine::utohexstr(NextAvailableAddress)
+ << " conflicts with ELF segment at 0x"
+ << Twine::utohexstr(Phdr.p_vaddr) << "\n";
+ }
}
}
}
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