[safestack] Do not link SafeStack runtime for musl environments

[mlemay-intel]

Summary

Musl libc provides runtime support for SafeStack, so the default
SafeStack library from compiler-rt is not needed.

[eugenis]

Test, please.
Where is this runtime support implemented? Some platform's libc, or an external library?

[mlemay-intel]

In D19170#402861, @eugenis wrote:

Test, please.

Do you know of any examples of the sort of test that you would like to see for a feature like this?

Where is this runtime support implemented? Some platform's libc, or an external library?

In my experience, supporting a separate stack segment seems to require a modified libc. The whole program, including libc routines, needs to be recompiled to direct memory accesses to the appropriate segment. This requires setting up an unsafe stack early enough that those recompiled routines can run successfully.

[eugenis]

In D19170#402939, @mlemay-intel wrote:

In D19170#402861, @eugenis wrote:

Test, please.

Do you know of any examples of the sort of test that you would like to see for a feature like this?

test/Driver/sanitizer-ld.c

[mlemay-intel]

Add test.

[eugenis]

LGTM

[Eugene.Zelenko]

Looks like patch was not committed.

[mlemay-intel]

In D19170#551426, @Eugene.Zelenko wrote:

Looks like patch was not committed.

This patch, D17092, D17094, and D17095 are all interdependent. I think it makes sense to wait until all four are approved so that they can all be committed together.

[Eugene.Zelenko]

Please add dependencies to Differential revisions, so reasons for holding will be clear.

[mlemay-intel]

Disabled linking of the compiler-rt SafeStack runtime library for musl
environments rather than for targets that use the separate stack segment
feature. This reflects changes in my proposed musl libc patches to add
architecture-independent support for storing USP in the TCB.

lib/Driver/Tools.cpp

if (SanArgs.needsTsanRt()) {
     if (SanArgs.linkCXXRuntimes())
       StaticRuntimes.push_back("tsan_cxx");
   }
   if (SanArgs.needsUbsanRt()) {
     StaticRuntimes.push_back("ubsan_standalone");
     if (SanArgs.linkCXXRuntimes())
       StaticRuntimes.push_back("ubsan_standalone_cxx");
   }
-  if (SanArgs.needsSafeStackRt())
+  if (SanArgs.needsSafeStackRt() && !TC.getTriple().isMusl())
     StaticRuntimes.push_back("safestack");
   if (SanArgs.needsCfiRt())
     StaticRuntimes.push_back("cfi");
   if (SanArgs.needsCfiDiagRt()) {
     StaticRuntimes.push_back("cfi_diag");
     if (SanArgs.linkCXXRuntimes())
       StaticRuntimes.push_back("ubsan_standalone_cxx");
   }

test/Driver/sanitizer-ld.c

 // RUN:   | FileCheck --check-prefix=CHECK-SAFESTACK-LINUX %s
 //
 // CHECK-SAFESTACK-LINUX: "{{(.*[^-.0-9A-Z_a-z])?}}ld{{(.exe)?}}"
 // CHECK-SAFESTACK-LINUX-NOT: "-lc"
 // CHECK-SAFESTACK-LINUX: libclang_rt.safestack-x86_64.a"
 // CHECK-SAFESTACK-LINUX: "-lpthread"
 // CHECK-SAFESTACK-LINUX: "-ldl"
 
+// RUN: %clang -no-canonical-prefixes %s -### -o %t.o 2>&1 \
+// RUN:     -target i386-unknown-linux-musl -fsanitize=safe-stack \
+// RUN:     --sysroot=%S/Inputs/basic_linux_tree \
+// RUN:   | FileCheck --check-prefix=CHECK-SAFESTACK-MUSL32 %s
+//
+// CHECK-SAFESTACK-MUSL32: "{{(.*[^-.0-9A-Z_a-z])?}}ld{{(.exe)?}}"
+// CHECK-SAFESTACK-MUSL32-NOT: libclang_rt.safestack-i386.a"
+
+// RUN: %clang -no-canonical-prefixes %s -### -o %t.o 2>&1 \
+// RUN:     -target x86_64-unknown-linux-musl -fsanitize=safe-stack \
+// RUN:     --sysroot=%S/Inputs/basic_linux_tree \
+// RUN:   | FileCheck --check-prefix=CHECK-SAFESTACK-MUSL64 %s
+//
+// CHECK-SAFESTACK-MUSL64: "{{(.*[^-.0-9A-Z_a-z])?}}ld{{(.exe)?}}"
+// CHECK-SAFESTACK-MUSL64-NOT: libclang_rt.safestack-x86_64.a"
+
 // RUN: %clang -fsanitize=cfi -fsanitize-stats %s -### -o %t.o 2>&1 \
 // RUN:     -target x86_64-unknown-linux \
 // RUN:     --sysroot=%S/Inputs/basic_linux_tree \
 // RUN:   | FileCheck --check-prefix=CHECK-CFI-STATS-LINUX %s
 // CHECK-CFI-STATS-LINUX: "{{.*}}ld{{(.exe)?}}"
 // CHECK-CFI-STATS-LINUX: "-whole-archive" "{{[^"]*}}libclang_rt.stats_client-x86_64.a" "-no-whole-archive"
 // CHECK-CFI-STATS-LINUX-NOT: "-whole-archive"
 // CHECK-CFI-STATS-LINUX: "{{[^"]*}}libclang_rt.stats-x86_64.a"