mirror of
https://github.com/tinygo-org/tinygo.git
synced 2026-08-03 18:47:47 +00:00
Ayke van Laethem
b31281a5b6
Previously we used to scan between _edata and _end. This is not correct: the .data section starts *before* _edata. Fixing this would mean changing _edata to _etext, but that didn't quite work either. It appears that there are inaccessible pages between _etext and _end on ARM. Therefore, a different solution was needed. What I've implemented is similar to Windows and MacOS: namely, finding writable segments by parsing the program header of the currently running program. It's a lot more verbose, but it should be correct on all architectures. It probably also reduces the globals to scan to those that _really_ need to be scanned. This bug didn't result in issues in CI, but did result in a bug in the recover branch: https://github.com/tinygo-org/tinygo/pull/2331. This patch fixes this bug.
124 lines
3.2 KiB
Go
124 lines
3.2 KiB
Go
//go:build linux && !baremetal && !nintendoswitch && !wasi
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// +build linux,!baremetal,!nintendoswitch,!wasi
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package runtime
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// This file is for systems that are _actually_ Linux (not systems that pretend
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// to be Linux, like baremetal systems).
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import "unsafe"
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const GOOS = "linux"
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const (
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// See https://github.com/torvalds/linux/blob/master/include/uapi/asm-generic/mman-common.h
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flag_PROT_READ = 0x1
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flag_PROT_WRITE = 0x2
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flag_MAP_PRIVATE = 0x2
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flag_MAP_ANONYMOUS = 0x20
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)
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// Source: https://github.com/torvalds/linux/blob/master/include/uapi/linux/time.h
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const (
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clock_REALTIME = 0
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clock_MONOTONIC_RAW = 4
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)
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// For the definition of the various header structs, see:
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// https://refspecs.linuxfoundation.org/elf/elf.pdf
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// Also useful:
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// https://en.wikipedia.org/wiki/Executable_and_Linkable_Format
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type elfHeader struct {
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ident_magic uint32
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ident_class uint8
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ident_data uint8
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ident_version uint8
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ident_osabi uint8
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ident_abiversion uint8
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_ [7]byte // reserved
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filetype uint16
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machine uint16
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version uint32
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entry uintptr
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phoff uintptr
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shoff uintptr
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flags uint32
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ehsize uint16
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phentsize uint16
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phnum uint16
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shentsize uint16
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shnum uint16
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shstrndx uint16
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}
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type elfProgramHeader64 struct {
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_type uint32
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flags uint32
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offset uintptr
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vaddr uintptr
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paddr uintptr
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filesz uintptr
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memsz uintptr
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align uintptr
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}
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type elfProgramHeader32 struct {
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_type uint32
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offset uintptr
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vaddr uintptr
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paddr uintptr
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filesz uintptr
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memsz uintptr
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flags uint32
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align uintptr
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}
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// ELF header of the currently running process.
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//
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//go:extern __ehdr_start
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var ehdr_start elfHeader
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// markGlobals marks all globals, which are reachable by definition.
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// It parses the ELF program header to find writable segments.
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func markGlobals() {
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// Relevant constants from the ELF specification.
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// See: https://refspecs.linuxfoundation.org/elf/elf.pdf
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const (
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PT_LOAD = 1
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PF_W = 0x2 // program flag: write access
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)
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headerPtr := unsafe.Pointer(uintptr(unsafe.Pointer(&ehdr_start)) + ehdr_start.phoff)
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for i := 0; i < int(ehdr_start.phnum); i++ {
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// Look for a writable segment and scan its contents.
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// There is a little bit of duplication here, which is unfortunate. But
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// the alternative would be to put elfProgramHeader in separate files
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// which is IMHO a lot uglier. If only the ELF spec was consistent
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// between 32-bit and 64-bit...
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if TargetBits == 64 {
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header := (*elfProgramHeader64)(headerPtr)
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if header._type == PT_LOAD && header.flags&PF_W != 0 {
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start := header.vaddr
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end := start + header.memsz
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markRoots(start, end)
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}
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} else {
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header := (*elfProgramHeader32)(headerPtr)
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if header._type == PT_LOAD && header.flags&PF_W != 0 {
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start := header.vaddr
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end := start + header.memsz
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markRoots(start, end)
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}
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}
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headerPtr = unsafe.Pointer(uintptr(headerPtr) + uintptr(ehdr_start.phentsize))
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}
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}
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//export getpagesize
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func libc_getpagesize() int
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//go:linkname syscall_Getpagesize syscall.Getpagesize
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func syscall_Getpagesize() int {
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return libc_getpagesize()
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}
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