sys/syz-extract: extract constants from ELF

Add a second mode that extracts constant values from
ELF object, instead of running the executable.
This allows to not (1) link binaries, (2) use proper cross-compiler.
It finally fixes 386/arm extracts for my distro.
Hopefully not makes things worse for others,
should generally be safer/more reliable.
The current mode is left b/c I can't test all OSes,
windows binaries are not ELF, so we may need it anyway.
But later we may switch more OSes to this new mode
if they break (fuchsia?).

1 files changed, 7 insertions, 23 deletions

diff --git a/sys/syz-extract/linux.go b/sys/syz-extract/linux.go
index 4c759a19d..b4bfd0b1e 100644
--- a/sys/syz-extract/linux.go
+++ b/sys/syz-extract/linux.go
@@ -5,7 +5,6 @@ package main
 
 import (
 	"fmt"
-	"os/exec"
 	"path/filepath"
 	"runtime"
 	"strings"
@@ -111,13 +110,6 @@ func (*linux) prepareArch(arch *Arch) error {
 }
 
 func (*linux) processFile(arch *Arch, info *compiler.ConstInfo) (map[string]uint64, map[string]bool, error) {
-	arch.once.Do(func() {
-		arch.cc = "gcc"
-		if !checkCompiler("gcc", arch.target.CFlags) &&
-			checkCompiler("clang", arch.target.CFlags) {
-			arch.cc = "clang"
-		}
-	})
 	headerArch := arch.target.KernelHeaderArch
 	sourceDir := arch.sourceDir
 	buildDir := arch.buildDir
@@ -143,7 +135,7 @@ func (*linux) processFile(arch *Arch, info *compiler.ConstInfo) (map[string]uint
 		"-I" + buildDir + "/syzkaller",
 		"-include", sourceDir + "/include/linux/kconfig.h",
 	}
-	args = append(args, arch.target.CFlags...)
+	args = append(args, arch.target.CrossCFlags...)
 	for _, incdir := range info.Incdirs {
 		args = append(args, "-I"+sourceDir+"/"+incdir)
 	}
@@ -152,14 +144,12 @@ func (*linux) processFile(arch *Arch, info *compiler.ConstInfo) (map[string]uint
 			args = append(args, "-I"+dir)
 		}
 	}
-	const addSource = `
-#include <asm/unistd.h>
-unsigned long phys_base;
-#ifndef __phys_addr
-unsigned long __phys_addr(unsigned long addr) { return 0; }
-#endif
-`
-	res, undeclared, err := extract(info, arch.cc, args, addSource, true, false)
+	params := &extractParams{
+		AddSource:      "#include <asm/unistd.h>",
+		ExtractFromELF: true,
+	}
+	cc := arch.target.CCompilerPrefix + "gcc"
+	res, undeclared, err := extract(info, cc, args, params)
 	if err != nil {
 		return nil, nil, err
 	}
@@ -179,9 +169,3 @@ unsigned long __phys_addr(unsigned long addr) { return 0; }
 	}
 	return res, undeclared, nil
 }
-
-func checkCompiler(cc string, args []string) bool {
-	cmd := exec.Command(cc, append(args, "-x", "c", "-", "-o", "/dev/null")...)
-	cmd.Stdin = strings.NewReader("int main(){}")
-	return cmd.Run() == nil
-}