[lld] 40a42f9 - [ELF] Make SORT_INIT_PRIORITY support .ctors.N
Fangrui Song via llvm-commits
llvm-commits at lists.llvm.org
Thu Nov 12 08:56:18 PST 2020
Author: Fangrui Song
Date: 2020-11-12T08:56:12-08:00
New Revision: 40a42f9f3fe9bf34f2d365705e72f12960cbb16c
URL: https://github.com/llvm/llvm-project/commit/40a42f9f3fe9bf34f2d365705e72f12960cbb16c
DIFF: https://github.com/llvm/llvm-project/commit/40a42f9f3fe9bf34f2d365705e72f12960cbb16c.diff
LOG: [ELF] Make SORT_INIT_PRIORITY support .ctors.N
Input sections `.ctors/.ctors.N` may go to either the output section `.init_array` or the output section `.ctors`:
* output `.ctors`: currently we sort them by name. This patch changes to sort by priority from high to low. If N in `.ctors.N` is in the form of %05u, there is no semantic difference. Actually GCC and Clang do use %05u. (In the test `ctors_dtors_priority.s` and Gold's test `gold/testsuite/script_test_14.s`, we can see %03u, but they are not really produced by compilers.)
* output `.init_array`: users can provide an input section description `SORT_BY_INIT_PRIORITY(.init_array.* .ctors.*)` to mix `.init_array.*` and `.ctors.*`. This can make .init_array.N and .ctors.(65535-N) interchangeable.
With this change, users can mix `.ctors.N` and `.init_array.N` in `.init_array` (PR44698 and PR48096) with linker scripts. As an example:
```
SECTIONS {
.init_array : {
*(SORT_BY_INIT_PRIORITY(.init_array.* .ctors.*))
*(.init_array EXCLUDE_FILE (*crtbegin.o *crtbegin?.o *crtend.o *crtend?.o ) .ctors)
}
} INSERT AFTER .fini_array;
SECTIONS {
.fini_array : {
*(SORT_BY_INIT_PRIORITY(.fini_array.* .dtors.*))
*(.fini_array EXCLUDE_FILE (*crtbegin.o *crtbegin?.o *crtend.o *crtend?.o ) .dtors)
}
} INSERT BEFORE .init_array;
```
Reviewed By: psmith
Differential Revision: https://reviews.llvm.org/D91187
Added:
Modified:
lld/ELF/OutputSections.cpp
lld/test/ELF/linkerscript/sort-init.s
Removed:
################################################################################
diff --git a/lld/ELF/OutputSections.cpp b/lld/ELF/OutputSections.cpp
index 518af1ee0548..5eea3bc8f6a5 100644
--- a/lld/ELF/OutputSections.cpp
+++ b/lld/ELF/OutputSections.cpp
@@ -447,19 +447,19 @@ static bool isCrtend(StringRef s) {
return std::regex_match(s.begin(), s.end(), re);
}
-// .ctors and .dtors are sorted by this priority from highest to lowest.
+// .ctors and .dtors are sorted by this order:
//
-// 1. The section was contained in crtbegin (crtbegin contains
-// some sentinel value in its .ctors and .dtors so that the runtime
-// can find the beginning of the sections.)
+// 1. .ctors/.dtors in crtbegin (which contains a sentinel value -1).
+// 2. The section is named ".ctors" or ".dtors" (priority: 65536).
+// 3. The section has an optional priority value in the form of ".ctors.N" or
+// ".dtors.N" where N is a number in the form of %05u (priority: 65535-N).
+// 4. .ctors/.dtors in crtend (which contains a sentinel value 0).
//
-// 2. The section has an optional priority value in the form of ".ctors.N"
-// or ".dtors.N" where N is a number. Unlike .{init,fini}_array,
-// they are compared as string rather than number.
-//
-// 3. The section is just ".ctors" or ".dtors".
-//
-// 4. The section was contained in crtend, which contains an end marker.
+// For 2 and 3, the sections are sorted by priority from high to low, e.g.
+// .ctors (65536), .ctors.00100 (65436), .ctors.00200 (65336). In GNU ld's
+// internal linker scripts, the sorting is by string comparison which can
+// achieve the same goal given the optional priority values are of the same
+// length.
//
// In an ideal world, we don't need this function because .init_array and
// .ctors are duplicate features (and .init_array is newer.) However, there
@@ -474,13 +474,7 @@ static bool compCtors(const InputSection *a, const InputSection *b) {
bool endB = isCrtend(b->file->getName());
if (endA != endB)
return endB;
- StringRef x = a->name;
- StringRef y = b->name;
- assert(x.startswith(".ctors") || x.startswith(".dtors"));
- assert(y.startswith(".ctors") || y.startswith(".dtors"));
- x = x.substr(6);
- y = y.substr(6);
- return x < y;
+ return getPriority(a->name) > getPriority(b->name);
}
// Sorts input sections by the special rules for .ctors and .dtors.
@@ -492,16 +486,17 @@ void OutputSection::sortCtorsDtors() {
llvm::stable_sort(isd->sections, compCtors);
}
-// If an input string is in the form of "foo.N" where N is a number,
-// return N. Otherwise, returns 65536, which is one greater than the
-// lowest priority.
+// If an input string is in the form of "foo.N" where N is a number, return N
+// (65535-N if .ctors.N or .dtors.N). Otherwise, returns 65536, which is one
+// greater than the lowest priority.
int elf::getPriority(StringRef s) {
size_t pos = s.rfind('.');
if (pos == StringRef::npos)
return 65536;
- int v;
- if (!to_integer(s.substr(pos + 1), v, 10))
- return 65536;
+ int v = 65536;
+ if (to_integer(s.substr(pos + 1), v, 10) &&
+ (pos == 6 && (s.startswith(".ctors") || s.startswith(".dtors"))))
+ v = 65535 - v;
return v;
}
diff --git a/lld/test/ELF/linkerscript/sort-init.s b/lld/test/ELF/linkerscript/sort-init.s
index dd030ace2efb..0a349fd9e57f 100644
--- a/lld/test/ELF/linkerscript/sort-init.s
+++ b/lld/test/ELF/linkerscript/sort-init.s
@@ -1,26 +1,43 @@
# REQUIRES: x86
-# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t1.o
-# RUN: echo "SECTIONS { .init_array : { *(SORT_BY_INIT_PRIORITY(.init_array.* foo*)) } }" > %t1.script
-# RUN: ld.lld --script %t1.script %t1.o -o %t2
-# RUN: llvm-objdump -s %t2 | FileCheck %s
+## Test SORT_BY_INIT_PRIORITY can be used to convert .ctors into .init_array
-# CHECK: Contents of section .init_array:
-# CHECK-NEXT: 03020000 00060000 010405
+# RUN: split-file %s %t
+# RUN: llvm-mc -filetype=obj -triple=x86_64 %t/asm -o %t.o
+# RUN: ld.lld -T %t/lds %t.o -o %t.out
+# RUN: llvm-readelf -x .init_array %t.out | FileCheck %s
+# CHECK: Hex dump of section '.init_array':
+# CHECK-NEXT: 0x00000001 00010203 04050607
+
+#--- asm
.globl _start
_start:
nop
.section foo, "aw", @init_array
- .byte 6
-.section .init_array, "aw", @init_array
- .align 8
- .byte 1
-.section .init_array.100, "aw", @init_array
- .long 2
-.section .init_array.5, "aw", @init_array
+ .byte 5
+
+.section .ctors.65435, "a"
.byte 3
-.section .init_array, "aw", @init_array
+.section .init_array.100, "aw", @init_array
.byte 4
+
+.section .init_array.7, "aw", @init_array
+ .byte 2
+.section .ctors.65529,"a"
+ .byte 1
+.section .init_array.5, "aw", @init_array
+ .byte 0
+
.section .init_array, "aw", @init_array
- .byte 5
+ .byte 6
+.section .ctors, "a"
+ .byte 7
+
+#--- lds
+SECTIONS {
+ .init_array : {
+ *(SORT_BY_INIT_PRIORITY(.init_array.* .ctors.*) SORT_BY_INIT_PRIORITY(foo*))
+ *(.init_array .ctors)
+ }
+}
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