[llvm] 73a9dfc - MC: make section classification a bit more thorough

[Saleem Abdulrasool via llvm-commits]

Author: Saleem Abdulrasool
Date: 2022-08-19T16:45:41Z
New Revision: 73a9dfcee24df959b59a46d75dcbdc0bcfb50fe6

URL: https://github.com/llvm/llvm-project/commit/73a9dfcee24df959b59a46d75dcbdc0bcfb50fe6
DIFF: https://github.com/llvm/llvm-project/commit/73a9dfcee24df959b59a46d75dcbdc0bcfb50fe6.diff

LOG: MC: make section classification a bit more thorough

This does *NOT* change the emitted section flags in any way.  This only
impacts the internal classification of sections.

Extend the section classification in LLVM for ELF targets.  This has one
important change: we now classify sections as text by default rather
than readonly.  This matches the behaviour for GAS better.

Ensure that any section that has a writable attribute set is not treated
as readonly.  We also special case any section named `.debug_` which is
reserved for DWARF as metadata.  In the case none of the attributes are
set (or because no attributes were provided), consult the section name
for classification.  We match the well known names and classify the
section accordingly.  Any remaining section is now classified as text.

This change allows us to classify sections in the MC layer more
precisely which is needed for subsequent changes for handling target
specific behaviour.

Differential Revision: https://reviews.llvm.org/D131270
Reviewed By: @echristo

Added: 
    

Modified: 
    llvm/lib/MC/MCContext.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/lib/MC/MCContext.cpp b/llvm/lib/MC/MCContext.cpp
index 29597088a212e..eda266a55c8ec 100644
--- a/llvm/lib/MC/MCContext.cpp
+++ b/llvm/lib/MC/MCContext.cpp
@@ -564,8 +564,24 @@ MCSectionELF *MCContext::getELFSection(const Twine &Section, unsigned Type,
     Kind = SectionKind::getExecuteOnly();
   else if (Flags & ELF::SHF_EXECINSTR)
     Kind = SectionKind::getText();
-  else
+  else if (~Flags & ELF::SHF_WRITE)
     Kind = SectionKind::getReadOnly();
+  else if (Flags & ELF::SHF_TLS)
+    // FIXME: should we 
diff erentiate between SHT_PROGBITS and SHT_NOBITS?
+    Kind = SectionKind::getThreadData();
+  else if (CachedName.startswith(".debug_"))
+    Kind = SectionKind::getMetadata();
+  else
+    Kind = llvm::StringSwitch<SectionKind>(CachedName)
+               .Case(".bss", SectionKind::getBSS())
+               .Case(".data", SectionKind::getData())
+               .Case(".data1", SectionKind::getMergeable1ByteCString())
+               .Case(".data.rel.ro", SectionKind::getReadOnlyWithRel())
+               .Case(".rodata", SectionKind::getReadOnly())
+               .Case(".rodata1", SectionKind::getReadOnly())
+               .Case(".tbss", SectionKind::getThreadBSS())
+               .Case(".tdata", SectionKind::getThreadData())
+               .Default(SectionKind::getText());
 
   MCSectionELF *Result =
       createELFSectionImpl(CachedName, Type, Flags, Kind, EntrySize, GroupSym,