[ELF] Expand regions for gaps due to explicit address

[yodaldevoid]

Summary

If the dot gets moved by an explicit section address, an empty gap between sections could be created. The encompassing region for the section being parsed needs to be expanded to include the gap.

[MaskRay]

lld/test/ELF/linkerscript/section-gap-explicit-expr.test

7 ↗

(On Diff #213256)

single-dash long options are discouraged in llvm-objdump. Use -h or --section-headers. I would use llvm-readelf -S.

16 ↗

(On Diff #213256)

ORIGIN(REGION) is not important in this test. You can just write:

SECTIONS {
  .aaa_s 0 : { *(.aaa) } > REGION
  .bbb_s 0x14 : { *(.bbb) } > REGION
}

There is no need to copy out-of-order-section-in-region.test. How about renaming to memory-*? There are several memory region tests named memory-* now. It'd be ideal to have a single dedicated prefix for these tests.

[MaskRay]

lld/test/ELF/linkerscript/section-gap-explicit-expr.test

3 ↗

(On Diff #213256)

echo ".section .aaa, 'a'; .quad 0; ..."

4 ↗

(On Diff #213256)

-o %t.o

ld.lld ... %t.o -o %t

[yodaldevoid]

I have updated the diff and I believe I have addressed all concerns that were brought up.

[MaskRay]

LGTM

[yodaldevoid]

I do not have commit access so if someone else could commit this patch for me I would appreciate it.

[MaskRay]

In D65722#1616702, @yodaldevoid wrote:

I do not have commit access so if someone else could commit this patch for me I would appreciate it.

I can commit but I'd like @ruiu to take a look first.

lld/test/ELF/linkerscript/memory-gap-explicit-expr.test

8 ↗

(On Diff #213516)

Any particular reason the output section is .aaa_s while the input section is .aaa. I don't think that matters but it may make people puzzled

[yodaldevoid]

In D65722#1616707, @MaskRay wrote:

I can commit but I'd like @ruiu to take a look first.

Understandable.

lld/test/ELF/linkerscript/memory-gap-explicit-expr.test

8 ↗

(On Diff #213516)

I made it .aaa_s when debugging so that I could differentiate printouts referring to sections as defined in the "program" and sections as defined in the linker script.

[ruiu]

LGTM

I think this makes sense. Let me submit this tomorrow (I'm leaving now, and I don't want to take a risk to break buildbots.)

lld/trunk/ELF/LinkerScript.cpp

void LinkerScript::assignOffsets(OutputSection *sec) {
   ctx->memRegion = sec->memRegion;
   ctx->lmaRegion = sec->lmaRegion;
   if (ctx->memRegion)
     dot = ctx->memRegion->curPos;
 
   if ((sec->flags & SHF_ALLOC) && sec->addrExpr)
     setDot(sec->addrExpr, sec->location, false);
 
+  // If the address of the section has been moved forward by an explicit
+  // expression so that it now starts past the current curPos of the enclosing
+  // region, we need to expand the current region to account for the space
+  // between the previous section, if any, and the start of this section.
+  if (ctx->memRegion && ctx->memRegion->curPos < dot)
+    expandMemoryRegion(ctx->memRegion, dot - ctx->memRegion->curPos,
+                       ctx->memRegion->name, sec->name);
+
   switchTo(sec);
 
   if (sec->lmaExpr)
     ctx->lmaOffset = sec->lmaExpr().getValue() - dot;
 
   if (MemoryRegion *mr = sec->lmaRegion)
     ctx->lmaOffset = mr->curPos - dot;
 

lld/trunk/test/ELF/linkerscript/memory-gap-explicit-expr.test

+# REQUIRES: x86
+
+# RUN: echo '.section .aaa, "a"; .quad 0; .section .bbb, "a"; .quad 0;' \
+# RUN:   | llvm-mc -filetype=obj -triple=x86_64 - -o %t.o
+# RUN: ld.lld %t.o --script %s -o %t
+# RUN: llvm-readelf -S %t | FileCheck %s
+
+# CHECK: .aaa PROGBITS 0000000000000000 001000 000008
+# CHECK: .bbb PROGBITS 0000000000000014 001014 000008
+
+MEMORY {
+  REGION (rwx) : ORIGIN = 0x0000, LENGTH = 0x100
+}
+
+SECTIONS {
+  .aaa 0 : { *(.aaa) } > REGION
+  .bbb 0x14 : { *(.bbb) } > REGION
+}