From a9503c50b327ba5eb453a1b983d3a733fadc2735 Mon Sep 17 00:00:00 2001
From: Victor Michel <victor@optimyze.cloud>
Date: Wed, 19 Aug 2020 00:22:42 -0700
Subject: [PATCH] Add code

---
 .gitignore          |  1 +
 Makefile            | 14 ++++++++++++++
 README.md           | 10 ++++++++++
 main.go             | 38 ++++++++++++++++++++++++++++++++++++++
 test.sh             |  9 +++++++++
 testdata/.gitignore |  1 +
 testdata/Makefile   |  7 +++++++
 testdata/repro.c    |  8 ++++++++
 testdata/repro.ld   |  5 +++++
 9 files changed, 93 insertions(+)
 create mode 100644 .gitignore
 create mode 100644 Makefile
 create mode 100644 README.md
 create mode 100644 main.go
 create mode 100755 test.sh
 create mode 100644 testdata/.gitignore
 create mode 100644 testdata/Makefile
 create mode 100644 testdata/repro.c
 create mode 100644 testdata/repro.ld

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..4c7a225
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1 @@
+dwarf-relocation-golang-bug
diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..4daffd4
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,14 @@
+.PHONY: all test
+
+all: test
+
+testdata/repro:
+	cd testdata && make
+
+dwarf-relocation-golang-bug: main.go
+	go build
+
+test: testdata/repro dwarf-relocation-golang-bug
+	@echo
+	@echo "Running test"
+	@./test.sh
diff --git a/README.md b/README.md
new file mode 100644
index 0000000..8f312d0
--- /dev/null
+++ b/README.md
@@ -0,0 +1,10 @@
+This is a standalone repro case for https://github.com/golang/go/issues/40879
+
+* `testdata` contains logic to build an executable `testdata/repro` that:
+    * has a `.rela.debug_ranges` section
+    * has a DWARF DIE that uses DW_AT_ranges (to force this, I used a linker script to spread the code across 2 sections at different addresses)
+* `main.go` contains logic that prints the PC ranges of `testdata/repro`
+* `test.sh` will print the PC ranges using both the Go binary, and `llvm-dwarfdump`, to highlight the difference
+* `make` will compile all binaries and run `test.sh`
+
+Note: you need `llvm` installed (for `llvm-dwarfdump`). Alternatively you can change the test.sh script to use the regular `dwarfdump`.
diff --git a/main.go b/main.go
new file mode 100644
index 0000000..d5c49ae
--- /dev/null
+++ b/main.go
@@ -0,0 +1,38 @@
+package main
+
+import (
+	"debug/elf"
+	"fmt"
+	"log"
+)
+
+func main() {
+	file, err := elf.Open("testdata/repro")
+	if err != nil {
+		log.Fatal(err)
+	}
+	defer file.Close()
+
+	dw, err := file.DWARF()
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	reader := dw.Reader()
+
+	// The first entry will be the (only) CU
+	entry, err := reader.Next()
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	// Read PC ranges from DIE
+	ranges, err := dw.Ranges(entry)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	for i := range ranges {
+		fmt.Printf("[0x%x, 0x%x)\n", ranges[i][0], ranges[i][1])
+	}
+}
diff --git a/test.sh b/test.sh
new file mode 100755
index 0000000..8fc2e99
--- /dev/null
+++ b/test.sh
@@ -0,0 +1,9 @@
+#!/bin/bash -eu
+
+echo "Actual ranges:"
+llvm-dwarfdump testdata/repro --name=repro.c | grep -A2 DW_AT_ranges | tail -2 | sed 's/))/)/' | tr -d ' '
+
+echo
+echo "Ranges derived from Golang's debug/elf + debug/dwarf"
+./dwarf-relocation-golang-bug
+
diff --git a/testdata/.gitignore b/testdata/.gitignore
new file mode 100644
index 0000000..de86576
--- /dev/null
+++ b/testdata/.gitignore
@@ -0,0 +1 @@
+repro
diff --git a/testdata/Makefile b/testdata/Makefile
new file mode 100644
index 0000000..70589e3
--- /dev/null
+++ b/testdata/Makefile
@@ -0,0 +1,7 @@
+.PHONY: all
+
+repro: repro.c repro.ld
+# The following command will likely print a warning (about a missing -T option), which should be ignored.
+# Removing the warning would require passing a fully-fledged linker script to bypass gcc's default.
+	gcc -g $^ -Wl,--emit-relocs -o $@
+
diff --git a/testdata/repro.c b/testdata/repro.c
new file mode 100644
index 0000000..f16e299
--- /dev/null
+++ b/testdata/repro.c
@@ -0,0 +1,8 @@
+__attribute__((section(".coffee_section")))
+int coffee(void) {
+    return 0;
+}
+
+int main(int argc, char *argv[]) {
+	return 0;
+}
diff --git a/testdata/repro.ld b/testdata/repro.ld
new file mode 100644
index 0000000..670456e
--- /dev/null
+++ b/testdata/repro.ld
@@ -0,0 +1,5 @@
+SECTIONS
+{
+    . = 0xC0FFEE;
+    .coffee_section : {}
+}