[lld] [llvm] [LLD] Add support for two special OpenBSD sections (PR #97122)
John Ericson via llvm-commits
llvm-commits at lists.llvm.org
Wed Jul 10 07:19:56 PDT 2024
https://github.com/Ericson2314 updated https://github.com/llvm/llvm-project/pull/97122
>From 9da46ac6e78ee5557ec05c38c3bf69bd846118f8 Mon Sep 17 00:00:00 2001
From: John Ericson <John.Ericson at Obsidian.Systems>
Date: Sun, 30 Jun 2024 18:47:58 -0400
Subject: [PATCH 1/2] [LLMV] set OpenBSD's ELFOSABI by default
This matches what is done for FreeBSD.
OpenBSD has a few special program header types, and other such ELF
extensions. Setting the ELFOSABI like so will allow LLD to support them
without needlessly impacting non-OpenBSD ELFs.
Testing strategy matches 8738c5b0fe0a92a153d7c678f7b51cac05f48b35 /
D107748. Added one for FreeBSD too for good measure.
---
llvm/include/llvm/MC/MCELFObjectWriter.h | 2 ++
llvm/test/MC/ELF/osabi-freebsd.s | 2 ++
llvm/test/MC/ELF/osabi-openbsd.s | 2 ++
3 files changed, 6 insertions(+)
create mode 100644 llvm/test/MC/ELF/osabi-freebsd.s
create mode 100644 llvm/test/MC/ELF/osabi-openbsd.s
diff --git a/llvm/include/llvm/MC/MCELFObjectWriter.h b/llvm/include/llvm/MC/MCELFObjectWriter.h
index d7c223cdcc07f..12237094ad86a 100644
--- a/llvm/include/llvm/MC/MCELFObjectWriter.h
+++ b/llvm/include/llvm/MC/MCELFObjectWriter.h
@@ -78,6 +78,8 @@ class MCELFObjectTargetWriter : public MCObjectTargetWriter {
return ELF::ELFOSABI_FREEBSD;
case Triple::Solaris:
return ELF::ELFOSABI_SOLARIS;
+ case Triple::OpenBSD:
+ return ELF::ELFOSABI_OPENBSD;
default:
return ELF::ELFOSABI_NONE;
}
diff --git a/llvm/test/MC/ELF/osabi-freebsd.s b/llvm/test/MC/ELF/osabi-freebsd.s
new file mode 100644
index 0000000000000..0dbef293772e9
--- /dev/null
+++ b/llvm/test/MC/ELF/osabi-freebsd.s
@@ -0,0 +1,2 @@
+# RUN: llvm-mc -filetype obj -triple amd64-freebsd %s | llvm-readobj -hS - | FileCheck %s
+# CHECK: OS/ABI: FreeBSD
diff --git a/llvm/test/MC/ELF/osabi-openbsd.s b/llvm/test/MC/ELF/osabi-openbsd.s
new file mode 100644
index 0000000000000..f501dfa7bb126
--- /dev/null
+++ b/llvm/test/MC/ELF/osabi-openbsd.s
@@ -0,0 +1,2 @@
+# RUN: llvm-mc -filetype obj -triple amd64-openbsd %s | llvm-readobj -hS - | FileCheck %s
+# CHECK: OS/ABI: OpenBSD
>From 7f1f90c3a6e677c495dcb6feddf708f558ea3d72 Mon Sep 17 00:00:00 2001
From: deraadt <deraadt at openbsd.org>
Date: Fri, 7 Oct 2022 15:04:51 +0000
Subject: [PATCH 2/2] [LLD] Extend special OpenBSD support, but scope under
ELFOSABI
- Add support for `.openbsd.mutable`
(rebaser's note) adapted from:
https://github.com/openbsd/src/commit/bd249b5664da50f0178adea78250a7a0d8ea6566
New auto-coalescing sections removed
In the linkers, collect objects in section "openbsd.mutable" and place
them into a page-aligned region in the bss, with the right markers for
kernel/ld.so to identify the region and skip making it immutable. While
here, fix readelf/objdump versions to show all of this. ok miod kettenis
- Add support for `.openbsd.syscalls`
(rebaser's note) adapted from:
https://github.com/openbsd/src/commit/42a61acefa8b3288ff2163fb55e934a3fee39974
Collect .openbsd.syscalls sections into a new PT_OPENBSD_SYSCALLS
segment. This will be used soon to pin system calls to designated call
sites.
ok deraadt@
- Scope OpenBSD special section handling under that ELFOSABI
As a preexisting comment in `ELF/Writer.cpp` says:
> section names shouldn't be significant in ELF in spirit.
so scoping OSABI-specific magic name hacks to just the OSABI in
question limits the degree to which we deviate from that "spirit" for
all other OSABIs.
OpenBSD in particular is very fast moving, having added a number of
special sections, etc. in recent years. It is unclear how possible /
reasonable it is for upstream to implement all these features in any
event, but scoping like this at least mitigates the fallout for other
OSABIs systems which wish to be more slow-moving.
---
lld/ELF/ScriptParser.cpp | 2 ++
lld/ELF/Writer.cpp | 35 +++++++++++++++++++++++++++--------
lld/test/ELF/openbsd-phdr.s | 8 ++++++--
3 files changed, 35 insertions(+), 10 deletions(-)
diff --git a/lld/ELF/ScriptParser.cpp b/lld/ELF/ScriptParser.cpp
index db46263115242..41bd9a95053f7 100644
--- a/lld/ELF/ScriptParser.cpp
+++ b/lld/ELF/ScriptParser.cpp
@@ -1628,7 +1628,9 @@ unsigned ScriptParser::readPhdrType() {
.Case("PT_GNU_EH_FRAME", PT_GNU_EH_FRAME)
.Case("PT_GNU_STACK", PT_GNU_STACK)
.Case("PT_GNU_RELRO", PT_GNU_RELRO)
+ .Case("PT_OPENBSD_MUTABLE", PT_OPENBSD_MUTABLE)
.Case("PT_OPENBSD_RANDOMIZE", PT_OPENBSD_RANDOMIZE)
+ .Case("PT_OPENBSD_SYSCALLS", PT_OPENBSD_SYSCALLS)
.Case("PT_OPENBSD_WXNEEDED", PT_OPENBSD_WXNEEDED)
.Case("PT_OPENBSD_BOOTDATA", PT_OPENBSD_BOOTDATA)
.Default(-1);
diff --git a/lld/ELF/Writer.cpp b/lld/ELF/Writer.cpp
index bce3cd2de7ed2..22835e0d16502 100644
--- a/lld/ELF/Writer.cpp
+++ b/lld/ELF/Writer.cpp
@@ -601,10 +601,16 @@ static bool isRelroSection(const OutputSection *sec) {
// ELF in spirit. But in reality many linker features depend on
// magic section names.
StringRef s = sec->name;
- return s == ".data.rel.ro" || s == ".bss.rel.ro" || s == ".ctors" ||
- s == ".dtors" || s == ".jcr" || s == ".eh_frame" ||
- s == ".fini_array" || s == ".init_array" ||
- s == ".openbsd.randomdata" || s == ".preinit_array";
+
+ bool abiAgnostic = s == ".data.rel.ro" || s == ".bss.rel.ro" ||
+ s == ".ctors" || s == ".dtors" || s == ".jcr" ||
+ s == ".eh_frame" || s == ".fini_array" ||
+ s == ".init_array" || s == ".preinit_array";
+
+ bool abiSpecific =
+ config->osabi == ELFOSABI_OPENBSD && s == ".openbsd.randomdata";
+
+ return abiAgnostic || abiSpecific;
}
// We compute a rank for each section. The rank indicates where the
@@ -2273,10 +2279,23 @@ SmallVector<PhdrEntry *, 0> Writer<ELFT>::createPhdrs(Partition &part) {
addHdr(PT_GNU_EH_FRAME, part.ehFrameHdr->getParent()->getPhdrFlags())
->add(part.ehFrameHdr->getParent());
- // PT_OPENBSD_RANDOMIZE is an OpenBSD-specific feature. That makes
- // the dynamic linker fill the segment with random data.
- if (OutputSection *cmd = findSection(".openbsd.randomdata", partNo))
- addHdr(PT_OPENBSD_RANDOMIZE, cmd->getPhdrFlags())->add(cmd);
+ // Handle OpenBSD-specific section types for OpenBSD "OS ABI".
+ if (config->osabi == ELFOSABI_OPENBSD) {
+ // PT_OPENBSD_MUTABLE makes the dynamic linker fill the segment with
+ // zero data, like bss, but it can be treated differently.
+ if (OutputSection *cmd = findSection(".openbsd.mutable", partNo))
+ addHdr(PT_OPENBSD_MUTABLE, cmd->getPhdrFlags())->add(cmd);
+
+ // PT_OPENBSD_RANDOMIZE makes the dynamic linker fill the segment
+ // with random data.
+ if (OutputSection *cmd = findSection(".openbsd.randomdata", partNo))
+ addHdr(PT_OPENBSD_RANDOMIZE, cmd->getPhdrFlags())->add(cmd);
+
+ // PT_OPENBSD_SYSCALLS makes the kernel and dynamic linker register
+ // system call sites.
+ if (OutputSection *cmd = findSection(".openbsd.syscalls", partNo))
+ addHdr(PT_OPENBSD_SYSCALLS, cmd->getPhdrFlags())->add(cmd);
+ }
if (config->zGnustack != GnuStackKind::None) {
// PT_GNU_STACK is a special section to tell the loader to make the
diff --git a/lld/test/ELF/openbsd-phdr.s b/lld/test/ELF/openbsd-phdr.s
index 5ba0e031b2c26..c9b138d69ddf6 100644
--- a/lld/test/ELF/openbsd-phdr.s
+++ b/lld/test/ELF/openbsd-phdr.s
@@ -1,10 +1,10 @@
# REQUIRES: x86
# RUN: rm -rf %t && split-file %s %t && cd %t
-# RUN: llvm-mc -filetype=obj -triple=x86_64 randomdata.s -o randomdata.o
+# RUN: llvm-mc -filetype=obj -triple=x86_64-openbsd randomdata.s -o randomdata.o
# RUN: ld.lld randomdata.o -o randomdata
# RUN: llvm-readelf -S -l randomdata | FileCheck %s --check-prefix=RANDOMDATA
-# RUN: llvm-mc -filetype=obj -triple=x86_64 /dev/null -o wxneeded.o
+# RUN: llvm-mc -filetype=obj -triple=x86_64-openbsd /dev/null -o wxneeded.o
# RUN: ld.lld -z wxneeded wxneeded.o -o wxneeded
# RUN: llvm-readelf -l wxneeded | FileCheck %s --check-prefix=WXNEEDED
@@ -20,6 +20,8 @@
# RANDOMDATA: Type Offset VirtAddr PhysAddr FileSiz MemSiz Flg Align
# RANDOMDATA: OPENBSD_RANDOMIZE 0x[[O]] 0x[[ADDR]] 0x[[ADDR]] 0x000008 0x000008 R 0x1
# CHECK-NEXT: OPENBSD_BOOTDATA 0x000000 0x0000000000000000 0x0000000000000000 0x000000 0x000000 R 0
+# CHECK-NEXT: OPENBSD_MUTABLE 0x000000 0x0000000000000000 0x0000000000000000 0x000000 0x000000 R 0
+# CHECK-NEXT: OPENBSD_SYSCALLS 0x000000 0x0000000000000000 0x0000000000000000 0x000000 0x000000 R 0
# CHECK-NEXT: OPENBSD_WXNEEDED 0x000000 0x0000000000000000 0x0000000000000000 0x000000 0x000000 R 0
#--- randomdata.s
@@ -31,6 +33,8 @@ PHDRS {
text PT_LOAD FILEHDR PHDRS;
rand PT_OPENBSD_RANDOMIZE;
boot PT_OPENBSD_BOOTDATA;
+ mutable PT_OPENBSD_MUTABLE;
+ syscalls PT_OPENBSD_SYSCALLS;
wxneeded PT_OPENBSD_WXNEEDED;
}
SECTIONS {
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