Fix only TBSS sections causing empty segment

TBSS sections are special, they do not consume any virtual memory size
at load time, they incur a cost only when setting up size of the initial
TLS image by either libc or libpthread.

Creating a segment when a TBSS section is encountered causes linker to
create an empty segment.

Resolves #353

Change-Id: I0ef94d6ec9bf0bfdc60b29795effe9fc59fabaf7
Signed-off-by: Shankar Easwaran <[email protected]>

Author: quic-seaswara

lib/Target/CreateProgramHeaders.hpp

@@ -369,15 +369,16 @@ bool GNULDBackend::createProgramHdrs() {
     if (config().options().isOMagic())
       cur_flag = (cur_flag & ~llvm::ELF::PF_W);
 
-    // getSegmentFlag returns 0 if the section is not allocatable.
-    if ((cur_flag != prev_flag) && (isCurAlloc))
-      createPT_LOAD = true;
+    if (!cur->isTBSS()) {
+      if ((cur_flag != prev_flag) && (isCurAlloc))
+        createPT_LOAD = true;
 
-    if (linkerScriptHasMemoryCommand && (cur_mem_region != prev_mem_region))
-      createPT_LOAD = true;
+      if (linkerScriptHasMemoryCommand && (cur_mem_region != prev_mem_region))
+        createPT_LOAD = true;
 
-    if (linkerScriptHasMemoryCommand && (cur_mem_region != prev_mem_region))
-      createPT_LOAD = true;
+      if (linkerScriptHasMemoryCommand && (cur_mem_region != prev_mem_region))
+        createPT_LOAD = true;
+    }
 
     // If the current section is alloc section and if the previous section is
     // NOBITS and current is PROGBITS, we need to create a new segment.
@@ -408,7 +409,7 @@ bool GNULDBackend::createProgramHdrs() {
 
         // If Program headers are not specified and the vma difference is big
         // lets create a PT_LOAD to adjust the offset.
-        if (std::abs(vmaoffset) > (int64_t)segAlign)
+        if ((std::abs(vmaoffset) > (int64_t)segAlign) && (!cur->isTBSS()))
           createPT_LOAD = true;
       }
     }

test/Common/standalone/TLS/OnlyTBSS/Inputs/script.t

@@ -0,0 +1,14 @@
+MEMORY
+{
+  RAM (rw) : ORIGIN = 10000, LENGTH = 5000
+}
+
+SECTIONS {
+ .foo : { *(.text.foo) } > RAM
+ .empty : {} > RAM
+ tbss : { *(.tbss*) } > RAM
+ .empty : {} > RAM
+ .main : { *(.text.main) } > RAM
+ output_data : { BYTE(0x0) *(.data*) } > RAM
+ /DISCARD/ : { *(.riscv.attributes) }
+}

test/Common/standalone/TLS/OnlyTBSS/Inputs/scripttbssnewregion.t

@@ -0,0 +1,16 @@
+MEMORY
+{
+  RAM (rw) : ORIGIN = 10000, LENGTH = 5000
+  ROM (rw) : ORIGIN = 20000, LENGTH = 5000
+}
+
+SECTIONS {
+ .foo : { *(.text.foo) } > RAM
+ .empty : {} > RAM
+ tdata : { *(.tdata*) } > ROM
+ tbss : { *(.tbss*) } > ROM
+ .empty : {} > ROM
+ .main : { *(.text.main) } > ROM
+ output_data : { BYTE(0x0) *(.data*) } > ROM
+ /DISCARD/ : { *(.riscv.attributes) }
+}

test/Common/standalone/TLS/OnlyTBSS/Inputs/tls.c

@@ -0,0 +1,4 @@
+__thread int b = 0;
+int data = 100;
+int foo() { return 0; }
+int main() { return 0; }

test/Common/standalone/TLS/OnlyTBSS/OnlyTBSS.test

@@ -0,0 +1,14 @@
+UNSUPPORTED: ndk-build
+#---OnlyTBSS.test--------------------------- Executable  -----------------#
+#BEGIN_COMMENT
+# This tests that using TBSS only does not create an empty segment
+#END_COMMENT
+#START_TEST
+RUN: %clang %clangopts -c %p/Inputs/tls.c -o %t1.1.o -fdata-sections -ftls-model=local-exec -fPIE
+RUN: %link %linkopts  %t1.1.o -T %p/Inputs/script.t  -o %t.out --defsym __aeabi_read_tp=0
+RUN: %readelf -l -W %t.out | %filecheck %s -check-prefix=EMPTYLOAD
+RUN: %link %linkopts  %t1.1.o -T %p/Inputs/scripttbssnewregion.t  -o %t.out --defsym __aeabi_read_tp=0
+RUN: %readelf -l -W %t.out | %filecheck %s -check-prefix=EMPTYLOAD
+#END_TEST
+
+#EMPTYLOAD-NOT: LOAD {{.*}} {{.*}} {{.*}} 0x{{[0]+}} 0x{{[0]+}} {{.*}}