[llvm] 167338d - [AVR] correctly declare __do_copy_data and __do_clear_bss
Ayke van Laethem via llvm-commits
llvm-commits at lists.llvm.org
Sun Jan 8 09:56:35 PST 2023
Author: Ayke van Laethem
Date: 2023-01-08T18:56:06+01:00
New Revision: 167338de9687a8e65672001aa4c4f2e62cf45a76
URL: https://github.com/llvm/llvm-project/commit/167338de9687a8e65672001aa4c4f2e62cf45a76
DIFF: https://github.com/llvm/llvm-project/commit/167338de9687a8e65672001aa4c4f2e62cf45a76.diff
LOG: [AVR] correctly declare __do_copy_data and __do_clear_bss
These two symbols are declared in object files to indicate whether .data
needs to be copied from flash or .bss needs to be cleared. They are
supported on avr-gcc and reduce firmware size a bit, which is especially
important on very small chips.
I checked the behavior of avr-gcc and matched it as well as possible.
>From my investigation, it seems to work as follows:
__do_copy_data is set when the compiler finds a data symbol:
* without a section name
* with a section name starting with ".data" or ".gnu.linkonce.d"
* with a section name starting with ".rodata" or ".gnu.linkonce.r" and
flash and RAM are in the same address space
__do_clear_bss is set when the compiler finds a data symbol:
* without a section name
* with a section name that starts with .bss
Simply checking whether the calculated section name starts with ".data",
".rodata" or ".bss" should result in the same behavior.
Fixes: https://github.com/llvm/llvm-project/issues/58857
Differential Revision: https://reviews.llvm.org/D140830
Added:
llvm/test/CodeGen/AVR/no-clear-bss.ll
llvm/test/CodeGen/AVR/no-copy-data.ll
Modified:
llvm/lib/Target/AVR/AVRAsmPrinter.cpp
llvm/lib/Target/AVR/AVRDevices.td
llvm/lib/Target/AVR/AVRSubtarget.h
llvm/test/CodeGen/AVR/clear-bss.ll
Removed:
################################################################################
diff --git a/llvm/lib/Target/AVR/AVRAsmPrinter.cpp b/llvm/lib/Target/AVR/AVRAsmPrinter.cpp
index 9128674ff4899..897a45e9df4c7 100644
--- a/llvm/lib/Target/AVR/AVRAsmPrinter.cpp
+++ b/llvm/lib/Target/AVR/AVRAsmPrinter.cpp
@@ -19,6 +19,7 @@
#include "MCTargetDesc/AVRMCExpr.h"
#include "TargetInfo/AVRTargetInfo.h"
+#include "llvm/BinaryFormat/ELF.h"
#include "llvm/CodeGen/AsmPrinter.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineInstr.h"
@@ -28,11 +29,13 @@
#include "llvm/IR/Mangler.h"
#include "llvm/MC/MCContext.h"
#include "llvm/MC/MCInst.h"
+#include "llvm/MC/MCSectionELF.h"
#include "llvm/MC/MCStreamer.h"
#include "llvm/MC/MCSymbol.h"
#include "llvm/MC/TargetRegistry.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/raw_ostream.h"
+#include "llvm/Target/TargetLoweringObjectFile.h"
#define DEBUG_TYPE "avr-asm-printer"
@@ -229,21 +232,51 @@ void AVRAsmPrinter::emitXXStructor(const DataLayout &DL, const Constant *CV) {
}
bool AVRAsmPrinter::doFinalization(Module &M) {
+ const TargetLoweringObjectFile &TLOF = getObjFileLowering();
+ const AVRTargetMachine &TM = (const AVRTargetMachine &)MMI->getTarget();
+ const AVRSubtarget *SubTM = (const AVRSubtarget *)TM.getSubtargetImpl();
+
+ bool NeedsCopyData = false;
+ bool NeedsClearBSS = false;
+ for (const auto &GO : M.globals()) {
+ if (!GO.hasInitializer() || GO.hasAvailableExternallyLinkage())
+ // These globals aren't defined in the current object file.
+ continue;
+
+ if (GO.hasCommonLinkage()) {
+ // COMMON symbols are put in .bss.
+ NeedsClearBSS = true;
+ continue;
+ }
+
+ auto *Section = cast<MCSectionELF>(TLOF.SectionForGlobal(&GO, TM));
+ if (Section->getName().startswith(".data"))
+ NeedsCopyData = true;
+ else if (Section->getName().startswith(".rodata") && SubTM->hasPROGMEM())
+ // AVRs that have a separate PROGMEM (that's most AVRs) store .rodata
+ // sections in RAM.
+ NeedsCopyData = true;
+ else if (Section->getName().startswith(".bss"))
+ NeedsClearBSS = true;
+ }
+
MCSymbol *DoCopyData = OutContext.getOrCreateSymbol("__do_copy_data");
MCSymbol *DoClearBss = OutContext.getOrCreateSymbol("__do_clear_bss");
- // FIXME: We can disable __do_copy_data if there are no static RAM variables.
-
- OutStreamer->emitRawComment(
- " Declaring this symbol tells the CRT that it should");
- OutStreamer->emitRawComment(
- "copy all variables from program memory to RAM on startup");
- OutStreamer->emitSymbolAttribute(DoCopyData, MCSA_Global);
+ if (NeedsCopyData) {
+ OutStreamer->emitRawComment(
+ " Declaring this symbol tells the CRT that it should");
+ OutStreamer->emitRawComment(
+ "copy all variables from program memory to RAM on startup");
+ OutStreamer->emitSymbolAttribute(DoCopyData, MCSA_Global);
+ }
- OutStreamer->emitRawComment(
- " Declaring this symbol tells the CRT that it should");
- OutStreamer->emitRawComment("clear the zeroed data section on startup");
- OutStreamer->emitSymbolAttribute(DoClearBss, MCSA_Global);
+ if (NeedsClearBSS) {
+ OutStreamer->emitRawComment(
+ " Declaring this symbol tells the CRT that it should");
+ OutStreamer->emitRawComment("clear the zeroed data section on startup");
+ OutStreamer->emitSymbolAttribute(DoClearBss, MCSA_Global);
+ }
return AsmPrinter::doFinalization(M);
}
diff --git a/llvm/lib/Target/AVR/AVRDevices.td b/llvm/lib/Target/AVR/AVRDevices.td
index 8ecb0a1e7b12e..f2c8a2e7a71e7 100644
--- a/llvm/lib/Target/AVR/AVRDevices.td
+++ b/llvm/lib/Target/AVR/AVRDevices.td
@@ -65,6 +65,11 @@ def FeatureMOVW : SubtargetFeature<"movw", "m_hasMOVW", "true",
"The device supports the 16-bit MOVW "
"instruction">;
+// The device has a separate flash namespace that must be accessed using special
+// instructions like lpm.
+def FeaturePROGMEM : SubtargetFeature<"progmem", "m_hasPROGMEM", "true",
+ "The device has a separate flash namespace">;
+
// The device supports the `LPM` instruction, with implied destination being r0.
def FeatureLPM : SubtargetFeature<"lpm", "m_hasLPM", "true",
"The device supports the `LPM` instruction">;
@@ -156,7 +161,7 @@ def ELFArchXMEGA7 : ELFArch<"EF_AVR_ARCH_XMEGA7">;
// device should have.
def FamilyAVR0 : Family<"avr0", []>;
-def FamilyAVR1 : Family<"avr1", [FamilyAVR0, FeatureLPM, FeatureMMR]>;
+def FamilyAVR1 : Family<"avr1", [FamilyAVR0, FeatureLPM, FeaturePROGMEM, FeatureMMR]>;
def FamilyAVR2
: Family<"avr2",
@@ -192,13 +197,13 @@ def FamilyTiny
FeatureSmallStack]>;
def FamilyXMEGA3 : Family<"xmega3",
- [FamilyAVR0, FeatureLPM, FeatureIJMPCALL,
+ [FamilyAVR0, FeatureLPM, FeaturePROGMEM, FeatureIJMPCALL,
FeatureADDSUBIW, FeatureSRAM, FeatureJMPCALL,
FeatureMultiplication, FeatureMOVW, FeatureLPMX,
FeatureBREAK]>;
def FamilyXMEGA : Family<"xmega",
- [FamilyAVR0, FeatureLPM, FeatureIJMPCALL,
+ [FamilyAVR0, FeatureLPM, FeaturePROGMEM, FeatureIJMPCALL,
FeatureADDSUBIW, FeatureSRAM, FeatureJMPCALL,
FeatureMultiplication, FeatureMOVW, FeatureLPMX,
FeatureSPM, FeatureBREAK, FeatureEIJMPCALL,
diff --git a/llvm/lib/Target/AVR/AVRSubtarget.h b/llvm/lib/Target/AVR/AVRSubtarget.h
index ee16ed4062c46..10ae4d276f378 100644
--- a/llvm/lib/Target/AVR/AVRSubtarget.h
+++ b/llvm/lib/Target/AVR/AVRSubtarget.h
@@ -73,6 +73,7 @@ class AVRSubtarget : public AVRGenSubtargetInfo {
bool hasLPMX() const { return m_hasLPMX; }
bool hasELPM() const { return m_hasELPM; }
bool hasELPMX() const { return m_hasELPMX; }
+ bool hasPROGMEM() const { return m_hasPROGMEM; }
bool hasSPM() const { return m_hasSPM; }
bool hasSPMX() const { return m_hasSPMX; }
bool hasDES() const { return m_hasDES; }
@@ -127,6 +128,7 @@ class AVRSubtarget : public AVRGenSubtargetInfo {
bool m_hasLPMX;
bool m_hasELPM;
bool m_hasELPMX;
+ bool m_hasPROGMEM;
bool m_hasSPM;
bool m_hasSPMX;
bool m_hasDES;
diff --git a/llvm/test/CodeGen/AVR/clear-bss.ll b/llvm/test/CodeGen/AVR/clear-bss.ll
index 9c63815c098d6..a822610bea7d3 100644
--- a/llvm/test/CodeGen/AVR/clear-bss.ll
+++ b/llvm/test/CodeGen/AVR/clear-bss.ll
@@ -1,5 +1,5 @@
; RUN: llc < %s -march=avr | FileCheck %s
; CHECK: .globl __do_clear_bss
- at zeroed = internal constant [3 x i8] zeroinitializer
-
+ at zeroed = internal global [3 x i8] zeroinitializer
+ at common = common global i8 0
diff --git a/llvm/test/CodeGen/AVR/no-clear-bss.ll b/llvm/test/CodeGen/AVR/no-clear-bss.ll
new file mode 100644
index 0000000000000..4a257470f8e09
--- /dev/null
+++ b/llvm/test/CodeGen/AVR/no-clear-bss.ll
@@ -0,0 +1,8 @@
+; RUN: llc < %s -march=avr | FileCheck %s
+
+; CHECK: .globl __do_copy_data
+; CHECK-NOT: .globl __do_clear_bss
+
+ at str = internal global [3 x i8] c"foo"
+ at noinit = internal constant [3 x i8] zeroinitializer, section ".noinit"
+ at external = external constant [3 x i8]
diff --git a/llvm/test/CodeGen/AVR/no-copy-data.ll b/llvm/test/CodeGen/AVR/no-copy-data.ll
new file mode 100644
index 0000000000000..4875296c19aa4
--- /dev/null
+++ b/llvm/test/CodeGen/AVR/no-copy-data.ll
@@ -0,0 +1,8 @@
+; RUN: llc < %s -march=avr | FileCheck %s
+
+; CHECK-NOT: .globl __do_copy_data
+; CHECK: .globl __do_clear_bss
+
+ at noinit = internal global i8 5, section ".noinit"
+ at external = external global i8
+ at global = global i8 0
More information about the llvm-commits
mailing list