runtime: add vdso support for linux/amd64. Fixes issue 1933.

R=iant, imkrasin, krasin, iant, minux.ma, rsc, nigeltao, r, fullung
CC=golang-dev
https://golang.org/cl/6454046

src/pkg/runtime/runtime.c

@@ -61,11 +61,15 @@ static uint8**	argv;
 Slice os·Args;
 Slice syscall·envs;
 
+void (*runtime·sysargs)(int32, uint8**);
+
 void
 runtime·args(int32 c, uint8 **v)
 {
 	argc = c;
 	argv = v;
+	if(runtime·sysargs != nil)
+		runtime·sysargs(c, v);
 }
 
 int32 runtime·isplan9;

src/pkg/runtime/runtime.h

@@ -514,6 +514,7 @@ extern	int32	runtime·gcwaiting;		// gc is waiting to run
 int8*	runtime·goos;
 int32	runtime·ncpu;
 extern	bool	runtime·iscgo;
+extern  void (*runtime·sysargs)(int32, uint8**);
 
 /*
  * common functions and data

src/pkg/runtime/vdso_linux_amd64.c

+// Copyright 2012 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+#include "runtime.h"
+
+#define AT_SYSINFO_EHDR 33
+#define AT_NULL	0    /* End of vector */
+#define PT_LOAD	1    /* Loadable program segment */
+#define PT_DYNAMIC 2 /* Dynamic linking information */
+#define DT_NULL 0    /* Marks end of dynamic section */
+#define DT_STRTAB 5  /* Address of string table */
+#define DT_SYMTAB 6  /* Address of symbol table */
+#define DT_VERSYM 0x6ffffff0
+#define	DT_VERDEF 0x6ffffffc
+
+#define VER_FLG_BASE 0x1 /* Version definition of file itself */
+#define SHN_UNDEF 0      /* Undefined section */
+#define SHT_DYNSYM 11    /* Dynamic linker symbol table */
+#define STT_FUNC 2       /* Symbol is a code object */
+#define STB_GLOBAL 1     /* Global symbol */
+#define STB_WEAK 2       /* Weak symbol */
+
+/* How to extract and insert information held in the st_info field.  */
+#define ELF64_ST_BIND(val) (((byte) (val)) >> 4)
+#define ELF64_ST_TYPE(val) ((val) & 0xf)
+
+#define EI_NIDENT (16)
+
+typedef uint16 Elf64_Half;
+typedef uint32 Elf64_Word;
+typedef	int32  Elf64_Sword;
+typedef uint64 Elf64_Xword;
+typedef	int64  Elf64_Sxword;
+typedef uint64 Elf64_Addr;
+typedef uint64 Elf64_Off;
+typedef uint16 Elf64_Section;
+typedef Elf64_Half Elf64_Versym;
+
+
+typedef struct
+{
+	Elf64_Word st_name;
+	byte st_info;
+	byte st_other;
+	Elf64_Section st_shndx;
+	Elf64_Addr st_value;
+	Elf64_Xword st_size;
+} Elf64_Sym;
+
+typedef struct
+{
+	Elf64_Half vd_version; /* Version revision */
+	Elf64_Half vd_flags;   /* Version information */
+	Elf64_Half vd_ndx;     /* Version Index */
+	Elf64_Half vd_cnt;     /* Number of associated aux entries */
+	Elf64_Word vd_hash;    /* Version name hash value */
+	Elf64_Word vd_aux;     /* Offset in bytes to verdaux array */
+	Elf64_Word vd_next;    /* Offset in bytes to next verdef entry */
+} Elf64_Verdef;
+
+typedef struct
+{
+	byte e_ident[EI_NIDENT]; /* Magic number and other info */
+	Elf64_Half e_type;       /* Object file type */
+	Elf64_Half e_machine;    /* Architecture */
+	Elf64_Word e_version;    /* Object file version */
+	Elf64_Addr e_entry;      /* Entry point virtual address */
+	Elf64_Off e_phoff;       /* Program header table file offset */
+	Elf64_Off e_shoff;       /* Section header table file offset */
+	Elf64_Word e_flags;      /* Processor-specific flags */
+	Elf64_Half e_ehsize;     /* ELF header size in bytes */
+	Elf64_Half e_phentsize;  /* Program header table entry size */
+	Elf64_Half e_phnum;      /* Program header table entry count */
+	Elf64_Half e_shentsize;  /* Section header table entry size */
+	Elf64_Half e_shnum;      /* Section header table entry count */
+	Elf64_Half e_shstrndx;   /* Section header string table index */
+} Elf64_Ehdr;
+
+typedef struct
+{
+	Elf64_Word p_type;    /* Segment type */
+	Elf64_Word p_flags;   /* Segment flags */
+	Elf64_Off p_offset;   /* Segment file offset */
+	Elf64_Addr p_vaddr;   /* Segment virtual address */
+	Elf64_Addr p_paddr;   /* Segment physical address */
+	Elf64_Xword p_filesz; /* Segment size in file */
+	Elf64_Xword p_memsz;  /* Segment size in memory */
+	Elf64_Xword p_align;  /* Segment alignment */
+} Elf64_Phdr;
+
+typedef struct
+{
+	Elf64_Word sh_name;       /* Section name (string tbl index) */
+	Elf64_Word sh_type;       /* Section type */
+	Elf64_Xword sh_flags;     /* Section flags */
+	Elf64_Addr sh_addr;       /* Section virtual addr at execution */
+	Elf64_Off sh_offset;      /* Section file offset */
+	Elf64_Xword sh_size;      /* Section size in bytes */
+	Elf64_Word sh_link;       /* Link to another section */
+	Elf64_Word sh_info;       /* Additional section information */
+	Elf64_Xword sh_addralign; /* Section alignment */
+	Elf64_Xword sh_entsize;   /* Entry size if section holds table */
+} Elf64_Shdr;
+
+typedef struct
+{
+	Elf64_Sxword d_tag; /* Dynamic entry type */
+	union
+	{
+		Elf64_Xword d_val;  /* Integer value */
+		Elf64_Addr d_ptr;   /* Address value */
+	} d_un;
+} Elf64_Dyn;
+
+typedef struct
+{
+	Elf64_Word vda_name; /* Version or dependency names */
+	Elf64_Word vda_next; /* Offset in bytes to next verdaux entry */
+} Elf64_Verdaux;
+
+typedef struct
+{
+	uint64 a_type;        /* Entry type */
+	union
+	{
+		uint64 a_val; /* Integer value */
+	} a_un;
+} Elf64_auxv_t;
+
+
+typedef struct {
+	byte* name;
+	void** var_ptr;
+} symbol_key;
+
+typedef struct {
+	byte* version;
+	int32 ver_hash;
+} version_key;
+
+struct vdso_info {
+	bool valid;
+
+	/* Load information */
+	uintptr load_addr;
+	uintptr load_offset;  /* load_addr - recorded vaddr */
+
+	/* Symbol table */
+	int32 num_sym;
+	Elf64_Sym *symtab;
+	const byte *symstrings;
+
+	/* Version table */
+	Elf64_Versym *versym;
+	Elf64_Verdef *verdef;
+};
+
+static version_key linux26 = { (byte*)"LINUX_2.6", 0x3ae75f6 };
+
+// initialize with vsyscall fallbacks
+void* runtime·__vdso_time_sym = (void*)0xffffffffff600400ULL;
+void* runtime·__vdso_gettimeofday_sym = (void*)0xffffffffff600000ULL;
+
+#define SYM_KEYS_COUNT 2
+static symbol_key sym_keys[] = {
+	{ (byte*)"__vdso_time", &runtime·__vdso_time_sym },
+	{ (byte*)"__vdso_gettimeofday", &runtime·__vdso_gettimeofday_sym },
+};
+
+static void vdso_init_from_sysinfo_ehdr(struct vdso_info *vdso_info, Elf64_Ehdr* hdr) {
+	uint64 i;
+	bool found_vaddr = false;
+
+	vdso_info->load_addr = (uintptr) hdr;
+
+	Elf64_Phdr *pt = (Elf64_Phdr*)(vdso_info->load_addr + hdr->e_phoff);
+	Elf64_Shdr *sh = (Elf64_Shdr*)(vdso_info->load_addr + hdr->e_shoff);
+	Elf64_Dyn *dyn = 0;
+
+	for(i=0; i<hdr->e_shnum; i++) {
+		if(sh[i].sh_type == SHT_DYNSYM) {
+			vdso_info->num_sym = sh[i].sh_size / sizeof(Elf64_Sym);
+		}
+	}
+
+	// We need two things from the segment table: the load offset
+	// and the dynamic table.
+	for(i=0; i<hdr->e_phnum; i++) {
+		if(pt[i].p_type == PT_LOAD && found_vaddr == false) {
+			found_vaddr = true;
+			vdso_info->load_offset =	(uintptr)hdr
+				+ (uintptr)pt[i].p_offset
+				- (uintptr)pt[i].p_vaddr;
+		} else if(pt[i].p_type == PT_DYNAMIC) {
+			dyn = (Elf64_Dyn*)((uintptr)hdr + pt[i].p_offset);
+		}
+	}
+
+	if(found_vaddr == false || dyn == nil)
+		return;  // Failed
+
+	// Fish out the useful bits of the dynamic table.
+	for(i=0; dyn[i].d_tag!=DT_NULL; i++) {
+		switch(dyn[i].d_tag) {
+		case DT_STRTAB:
+			vdso_info->symstrings = (const byte *)
+				((uintptr)dyn[i].d_un.d_ptr
+				 + vdso_info->load_offset);
+			break;
+		case DT_SYMTAB:
+			vdso_info->symtab = (Elf64_Sym *)
+				((uintptr)dyn[i].d_un.d_ptr
+				 + vdso_info->load_offset);
+			break;
+		case DT_VERSYM:
+			vdso_info->versym = (Elf64_Versym *)
+				((uintptr)dyn[i].d_un.d_ptr
+				 + vdso_info->load_offset);
+			break;
+		case DT_VERDEF:
+			vdso_info->verdef = (Elf64_Verdef *)
+				((uintptr)dyn[i].d_un.d_ptr
+				 + vdso_info->load_offset);
+			break;
+		}
+	}
+	if(vdso_info->symstrings == nil || vdso_info->symtab == nil)
+		return;  // Failed
+
+	if(vdso_info->verdef == nil)
+		vdso_info->versym = 0;
+
+	// That's all we need.
+	vdso_info->valid = true;
+}
+
+static int32 vdso_find_version(struct vdso_info *vdso_info, version_key* ver) {
+	if(vdso_info->valid == false) {
+		return 0;
+	}
+	Elf64_Verdef *def = vdso_info->verdef;
+	while(true) {
+		if((def->vd_flags & VER_FLG_BASE) == 0) {
+			Elf64_Verdaux *aux = (Elf64_Verdaux*)((byte *)def + def->vd_aux);
+			if(def->vd_hash == ver->ver_hash &&
+				runtime·strcmp(ver->version, vdso_info->symstrings + aux->vda_name) == 0) {
+				return def->vd_ndx & 0x7fff;
+			}
+		}
+
+		if(def->vd_next == 0) {
+			break;
+		}
+		def = (Elf64_Verdef *)((byte *)def + def->vd_next);
+	}
+	return 0;
+}
+
+static void vdso_parse_symbols(struct vdso_info *vdso_info, int32 version) {
+	int32 i, j;
+
+	if(vdso_info->valid == false)
+		return;
+
+	for(i=0; i<vdso_info->num_sym; i++) {
+		Elf64_Sym *sym = &vdso_info->symtab[i];
+
+		// Check for a defined global or weak function w/ right name.
+		if(ELF64_ST_TYPE(sym->st_info) != STT_FUNC)
+			continue;
+		if(ELF64_ST_BIND(sym->st_info) != STB_GLOBAL &&
+			ELF64_ST_BIND(sym->st_info) != STB_WEAK)
+			continue;
+		if(sym->st_shndx == SHN_UNDEF)
+			continue;
+
+		for(j=0; j<SYM_KEYS_COUNT; j++) {
+			if(runtime·strcmp(sym_keys[j].name, vdso_info->symstrings + sym->st_name) != 0)
+				continue;
+
+			// Check symbol version.
+			if(vdso_info->versym != nil && version != 0
+				&& vdso_info->versym[i] & 0x7fff != version)
+				continue;
+
+			*sym_keys[j].var_ptr = (void *)(vdso_info->load_offset + sym->st_value);
+		}
+	}
+}
+
+static void
+runtime·linux_setup_vdso(int32 argc, uint8** argv)
+{
+	struct vdso_info vdso_info;
+
+	// skip argvc
+	byte **p = argv;
+	p = &p[argc+1];
+
+	// skip envp to get to ELF auxiliary vector.
+	for(; *p!=0; p++) {}
+
+	// skip NULL separator
+	p++;
+
+	// now, p points to auxv
+	Elf64_auxv_t *elf_auxv = (Elf64_auxv_t*) p;
+
+	for(int32 i=0; elf_auxv[i].a_type!=AT_NULL; i++) {
+		if(elf_auxv[i].a_type == AT_SYSINFO_EHDR) {
+			if(elf_auxv[i].a_un.a_val == 0) {
+				// Something went wrong
+				return;
+			}
+			vdso_init_from_sysinfo_ehdr(&vdso_info, (Elf64_Ehdr*)elf_auxv[i].a_un.a_val);
+			vdso_parse_symbols(&vdso_info, vdso_find_version(&vdso_info, &linux26));
+			return;
+		}
+	}
+}
+
+void (*runtime·sysargs)(int32, uint8**) = runtime·linux_setup_vdso;

src/pkg/syscall/asm_linux_amd64.s

@@ -108,7 +108,7 @@ ok2:
 TEXT ·Gettimeofday(SB),7,$0
 	MOVQ	8(SP), DI
 	MOVQ	$0, SI
-	MOVQ	$0xffffffffff600000, AX
+	MOVQ	runtime·__vdso_gettimeofday_sym(SB), AX
 	CALL	AX
 
 	CMPQ	AX, $0xfffffffffffff001
@@ -122,7 +122,7 @@ ok7:
 
 TEXT ·Time(SB),7,$0
 	MOVQ	8(SP), DI
-	MOVQ	$0xffffffffff600400, AX
+	MOVQ	runtime·__vdso_time_sym(SB), AX
 	CALL	AX
 	MOVQ	AX, 16(SP)  // tt
 	MOVQ	$0, 24(SP)  // errno