Split-stack support for cross-linking shared-libraries.

[grimar]

• x86-64-split-stack-prologue-adjust-success.s differs only in a white space. Please revert.
• It feels that x86-64-split-stack-prologue-adjust-shared.s can be simpler. Since you are testing the call of function from a shared library, I would expect one main file .s and one dso file with a single call from main .s perhaps. Can it be done in that way?

ELF/InputSection.cpp

920

You do not need curly braces here:

if (Defined *D = dyn_cast<Defined>(Rel.Sym))
  if (InputSection *IS = cast_or_null<InputSection>(D->Section))
    if (!IS || IS->getFile<ELFT>()->SplitStack)
      continue;

test/ELF/x86-64-split-stack-prologue-adjust-shared.s

20

Since this test case is new, I wonder if it really needs the duplicated and/or various calls,
I think this part was copy pasted and probably is excessive.

30

ldd -> lld

[saugustine]

Thanks for the feedback, please take another look if you would.

[saugustine]

Cleanup test case.

[saugustine]

ping?

[grimar]

test/ELF/x86-64-split-stack-prologue-adjust-shared.s

6

What I not understand is why do you need this file here?
You have a caller (x86-64-split-stack-prologue-adjust-shared.s) and a shared library (x86-64-split-stack-extra.s),
is not that enough for testing the call?

Also, why do you have to use -z notext below?

I was able to remove both the file and the option and test case still passed for me.
So could you please reduce it to minimal possible? That is the desired way to write the test cases we are trying to follow usually.

[saugustine]

Thanks for the review. I apologize for not producing something sufficiently minimal on the previous round.

[saugustine]

Further minimize the test case.

[grimar]

LGTM. Please wait for the Rui's opinion as well.

[ruiu]

LGTM

[saugustine]

Committed as rLLD339626

ELF/InputSection.cpp

void InputSectionBase::adjustSplitStackFunctionPrologues(uint8_t *Buf,
 
   for (Relocation &Rel : Relocations) {
     // Local symbols can't possibly be cross-calls, and should have been
     // resolved long before this line.
     if (Rel.Sym->isLocal())
       continue;
 
     // Ignore calls into the split-stack api.
-    Defined *D = cast<Defined>(Rel.Sym);
-    if (D->getName().startswith("__morestack")) {
-      if (D->getName().equals("__morestack"))
+    if (Rel.Sym->getName().startswith("__morestack")) {
+      if (Rel.Sym->getName().equals("__morestack"))
         MorestackCalls.push_back(&Rel);
       continue;
     }
 
     // A relocation to non-function isn't relevant. Sometimes
     // __morestack is not marked as a function, so this check comes
     // after the name check.
-    if (D->Type != STT_FUNC)
+    if (Rel.Sym->Type != STT_FUNC)
       continue;
 
-    // If the callee's-file was compiled with split stack, nothing to do.
-    auto *IS = cast_or_null<InputSection>(D->Section);
+    // If the callee's-file was compiled with split stack, nothing to do.  In
+    // this context, a "Defined" symbol is one "defined by the binary currently
+    // being produced". So an "undefined" symbol might be provided by a shared
+    // library. It is not possible to tell how such symbols were compiled, so be
+    // conservative.
+    if (Defined *D = dyn_cast<Defined>(Rel.Sym))
+      if (InputSection *IS = cast_or_null<InputSection>(D->Section))
         if (!IS || IS->getFile<ELFT>()->SplitStack)
           continue;
 
     if (enclosingPrologueAttempted(Rel.Offset, Prologues))
       continue;
 
     if (Defined *F = getEnclosingFunction<ELFT>(Rel.Offset)) {
       Prologues.insert(F);
       if (Target->adjustPrologueForCrossSplitStack(Buf + getOffset(F->Value),
                                                    End))
         continue;
       if (!getFile<ELFT>()->SomeNoSplitStack)
         error(lld::toString(this) + ": " + F->getName() +
-              " (with -fsplit-stack) calls " + D->getName() +
+              " (with -fsplit-stack) calls " + Rel.Sym->getName() +
               " (without -fsplit-stack), but couldn't adjust its prologue");
     }
   }
   switchMorestackCallsToMorestackNonSplit(Prologues, MorestackCalls);
 }
 
 template <class ELFT> void InputSection::writeTo(uint8_t *Buf) {
   if (Type == SHT_NOBITS)

test/ELF/x86-64-split-stack-prologue-adjust-shared.s

+# REQUIRES: x86
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %p/Inputs/x86-64-split-stack-extra.s -o %t2.o
+# RUN: ld.lld --defsym __morestack=0x100 --defsym __morestack_non_split=0x200 %t2.o -o %t4.so  -shared
+
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t1.o
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %p/Inputs/x86-64-split-stack-main.s -o %t3.o
+# RUN: ld.lld --defsym __morestack=0x100 --defsym __morestack_non_split=0x200 %t1.o %t3.o %t4.so -o %t -z notext 
+# RUN: llvm-objdump -d %t | FileCheck %s
+
+# For a cross .so call, make sure lld produced the conservative call to __morestack_non_split.
+# CHECK: prologue1_cross_so_call:
+# CHECK-NEXT: stc{{.*$}}
+# CHECK-NEXT: nopl{{.*$}}
+# CHECK: jae{{.*$}}
+# CHECK-NEXT: callq{{.*}}<__morestack_non_split>
+
+  .text
+
+  .global prologue1_cross_so_call
+  .type prologue1_cross_so_call,@function
+prologue1_cross_so_call:
+  cmp %fs:0x70,%rsp
+  jae 1f
+  callq __morestack
+  retq
+1:
+  callq split
+  retq
+  .size prologue1_cross_so_call,. - prologue1_cross_so_call
+
+  .section  .note.GNU-stack,"",@progbits
+  .section  .note.GNU-split-stack,"",@progbits