[ELF] - Teach input section wildcard patterns to recognize '?' meta character.

[grimar]

Summary

`?' - matches any single character
https://sourceware.org/binutils/docs/ld/Input-Section-Wildcards.html

This is used in few linker scripts I saw. Ex:

.init_array     :
  {
    KEEP (*(SORT_BY_INIT_PRIORITY(.init_array.*) SORT_BY_INIT_PRIORITY(.ctors.*)))
    KEEP (*(.init_array EXCLUDE_FILE (*crtbegin.o *crtbegin?.o *crtend.o *crtend?.o ) .ctors))
  }

[• rafael]

Testcase?

[grimar]

• Added testcase

[grimar]

• Fixed comment in testcase

[• rafael]

ELF/LinkerScript.cpp

66

Why rename S to W in the same commit?

[ruiu]

ELF/LinkerScript.cpp

58–63

I don't think we need examples because this pattern matching is familiar.

// Returns true if S matches T. S can contain DOS-style wildcard characters.
// The asterisk ('*') matches one or more characacters, and the question
// mark ('?') matches one character.

test/ELF/wildcards.s

1

If you create a new file, please move the existing test for '*' in linkerscript-sections.s to this file.

[grimar]

• Addressed review comments.

ELF/LinkerScript.cpp

66

We often rename the variables during common patches. See nothing ubnormal here. But reverted it back, if you think it is better to do separatelly.

test/ELF/wildcards.s

1

I can't do that. Those test uses those file source code.
I removed test from linkerscript-sections.s and added one additional for * here.

[• rafael]

ELF/LinkerScript.cpp

57–58

glob is probably a better known term than DOS-style wildcard.

[grimar]

ELF/LinkerScript.cpp

57–58

https://sourceware.org/binutils/docs/ld/Input-Section-Wildcards.html
In specs it just called "the wildcard patterns characters" I think.
At least there is a mention that "The wildcard patterns are like those used by the Unix shell." and below each special symbol named as character.

[• rafael]

ELF/LinkerScript.cpp

57–58

"those used by the Unix shell" == glob.

Please don't use DOS-style.

[ruiu]

ELF/LinkerScript.cpp

57–58

glob sounds fine.

[grimar]

• s/DOS-style wildcard characters/glob meta-characters

[• rafael]

LGTM with a nit. This patch is not changing what '*' does and should not change its description to say it doesn't match 0 characters.

ELF/LinkerScript.cpp

58

'*' can't really mach 0 characters?

[ruiu]

LGTM

ELF/LinkerScript.cpp

58

That's a good question, and I found that either the code or this comment is wrong. If my understanding is correct, '*' in this function matches zero-or-more. We need to fix either one.

ELF/LinkerScript.cpp

 int LinkerScript::compareSections(StringRef A, StringRef B) {
   auto E = SectionOrder.end();
   auto I = std::find(SectionOrder.begin(), E, A);
   auto J = std::find(SectionOrder.begin(), E, B);
   if (I == E || J == E)
     return 0;
   return I < J ? -1 : 1;
 }
 
-// Returns true if S matches T. S may contain a meta character '*'
-// which matches zero or more occurrences of any character.
-static bool matchStr(StringRef S, StringRef T) {
+// Returns true if wildcard pattern W matches T.
+// W may contain next meta characters:
+// '*' which matches zero or more occurrences of any character.
+// '?' matches any single character.
+// Ex: matchStr(".sec*", ".sec.1") == true
+// Ex: matchStr("crtbegin?.o", "crtbeginS.o") == true
+static bool matchStr(StringRef W, StringRef T) {
   for (;;) {
-    if (S.empty())
+    if (W.empty())
       return T.empty();
-    if (S[0] == '*') {
-      S = S.substr(1);
-      if (S.empty())
+    if (W[0] == '*') {
+      W = W.substr(1);
+      if (W.empty())
         // Fast path. If a pattern is '*', it matches anything.
         return true;
       for (size_t I = 0, E = T.size(); I < E; ++I)
-        if (matchStr(S, T.substr(I)))
+        if (matchStr(W, T.substr(I)))
           return true;
       return false;
     }
-    if (T.empty() || S[0] != T[0])
+    if (T.empty() || (W[0] != T[0] && W[0] != '?'))
       return false;
-    S = S.substr(1);
+    W = W.substr(1);
     T = T.substr(1);
   }
 }
 
 template <class ELFT> bool SectionRule::match(InputSectionBase<ELFT> *S) {
   return matchStr(SectionPattern, S->getSectionName());
 }
 

test/ELF/wildcards.s

+# REQUIRES: x86
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t
+
+## Default case: abc and abx included in text.
+# RUN: echo "SECTIONS { \
+# RUN:      .text : { *(.abc .abx) } }" > %t.script
+# RUN: ld.lld -o %t.out --script %t.script %t
+# RUN: llvm-objdump -section-headers %t.out | \
+# RUN:   FileCheck -check-prefix=SEC-DEFAULT %s
+# SEC-DEFAULT:      Sections:
+# SEC-DEFAULT-NEXT: Idx Name          Size      Address          Type
+# SEC-DEFAULT-NEXT:   0               00000000 0000000000000000
+# SEC-DEFAULT-NEXT:   1 .text         00000008 0000000000011000 TEXT DATA
+# SEC-DEFAULT-NEXT:   2 .abcd         00000004 0000000000011008 TEXT DATA
+# SEC-DEFAULT-NEXT:   3 .symtab       00000030 0000000000000000
+# SEC-DEFAULT-NEXT:   4 .shstrtab     00000027 0000000000000000
+# SEC-DEFAULT-NEXT:   5 .strtab       00000008 0000000000000000
+
+## Now replace the symbol with '?' and check that results are the same.
+# RUN: echo "SECTIONS { \
+# RUN:      .text : { *(.abc .ab?) } }" > %t.script
+# RUN: ld.lld -o %t.out --script %t.script %t
+# RUN: llvm-objdump -section-headers %t.out | \
+# RUN:   FileCheck -check-prefix=SEC-DEFAULT %s
+
+## Now see how replacing '?' with '*' will consume whole abcd.
+# RUN: echo "SECTIONS { \
+# RUN:      .text : { *(.abc .ab*) } }" > %t.script
+# RUN: ld.lld -o %t.out --script %t.script %t
+# RUN: llvm-objdump -section-headers %t.out | \
+# RUN:   FileCheck -check-prefix=SEC-ALL %s
+# SEC-ALL:      Sections:
+# SEC-ALL-NEXT: Idx Name          Size      Address          Type
+# SEC-ALL-NEXT:   0               00000000 0000000000000000
+# SEC-ALL-NEXT:   1 .text         0000000c 0000000000011000 TEXT DATA
+# SEC-ALL-NEXT:   2 .symtab       00000030 0000000000000000
+# SEC-ALL-NEXT:   3 .shstrtab     00000021 0000000000000000
+# SEC-ALL-NEXT:   4 .strtab       00000008 0000000000000000
+
+.text
+.section .abc,"ax",@progbits
+.long 0
+
+.text
+.section .abx,"ax",@progbits
+.long 0
+
+.text
+.section .abcd,"ax",@progbits
+.long 0
+
+.globl _start
+_start: