[v2,22/36] linux-user/i386: Add vdso and use it for sigreturn

diff --git a/linux-user/elfload.c b/linux-user/elfload.c
index ec3a854b44..7a598f9f76 100644
--- a/linux-user/elfload.c
+++ b/linux-user/elfload.c
@@ -276,12 +276,24 @@  static void elf_core_copy_regs(target_elf_gregset_t *regs, const CPUX86State *en
     (*regs)[15] = env->regs[R_ESP];
     (*regs)[16] = env->segs[R_SS].selector & 0xffff;
 }
-#endif
+
+/*
+ * i386 is the only target which supplies AT_SYSINFO for the vdso.
+ * All others only supply AT_SYSINFO_EHDR.
+ */
+#define DLINFO_ARCH_ITEMS 1
+#define ARCH_DLINFO       NEW_AUX_ENT(AT_SYSINFO, vdso_info->entry);
+
+#include "vdso.c.inc"
+
+#define vdso_image_info()    &vdso_image_info
+
+#endif /* TARGET_X86_64 */
 
 #define USE_ELF_CORE_DUMP
 #define ELF_EXEC_PAGESIZE       4096
 
-#endif
+#endif /* TARGET_I386 */
 
 #ifdef TARGET_ARM
 
diff --git a/linux-user/i386/signal.c b/linux-user/i386/signal.c
index 9894e7c9ac..8e4677e800 100644
--- a/linux-user/i386/signal.c
+++ b/linux-user/i386/signal.c
@@ -313,7 +313,7 @@  get_sigframe(struct target_sigaction *ka, CPUX86State *env, size_t frame_size)
 void setup_frame(int sig, struct target_sigaction *ka,
                  target_sigset_t *set, CPUX86State *env)
 {
-    abi_ulong frame_addr;
+    abi_ulong frame_addr, retcode_addr;
     struct sigframe *frame;
     int i;
 
@@ -335,19 +335,19 @@  void setup_frame(int sig, struct target_sigaction *ka,
     /* Set up to return from userspace.  If provided, use a stub
        already in userspace.  */
     if (ka->sa_flags & TARGET_SA_RESTORER) {
-        __put_user(ka->sa_restorer, &frame->pretcode);
+        retcode_addr = ka->sa_restorer;
     } else {
-        uint16_t val16;
-        abi_ulong retcode_addr;
-        retcode_addr = frame_addr + offsetof(struct sigframe, retcode);
-        __put_user(retcode_addr, &frame->pretcode);
-        /* This is popl %eax ; movl $,%eax ; int $0x80 */
-        val16 = 0xb858;
-        __put_user(val16, (uint16_t *)(frame->retcode+0));
+        /*
+         * This is popl %eax ; movl $,%eax ; int $0x80.
+         * This is no longer used, but is retained for ABI compatibility.
+         */
+        __put_user(0xb858, (uint16_t *)(frame->retcode+0));
         __put_user(TARGET_NR_sigreturn, (int *)(frame->retcode+2));
-        val16 = 0x80cd;
-        __put_user(val16, (uint16_t *)(frame->retcode+6));
+        __put_user(0x80cd, (uint16_t *)(frame->retcode+6));
+
+        retcode_addr = default_sigreturn;
     }
+    __put_user(retcode_addr, &frame->pretcode);
 
     /* Set up registers for signal handler */
     env->regs[R_ESP] = frame_addr;
@@ -373,7 +373,7 @@  void setup_rt_frame(int sig, struct target_sigaction *ka,
                     target_siginfo_t *info,
                     target_sigset_t *set, CPUX86State *env)
 {
-    abi_ulong frame_addr;
+    abi_ulong frame_addr, retcode_addr;
 #ifndef TARGET_X86_64
     abi_ulong addr;
 #endif
@@ -412,22 +412,23 @@  void setup_rt_frame(int sig, struct target_sigaction *ka,
     /* Set up to return from userspace.  If provided, use a stub
        already in userspace.  */
     if (ka->sa_flags & TARGET_SA_RESTORER) {
-        __put_user(ka->sa_restorer, &frame->pretcode);
+        retcode_addr = ka->sa_restorer;
     } else {
 #ifdef TARGET_X86_64
         /* For x86_64, SA_RESTORER is required ABI.  */
         goto give_sigsegv;
 #else
-        uint16_t val16;
-        addr = frame_addr + offsetof(struct rt_sigframe, retcode);
-        __put_user(addr, &frame->pretcode);
-        /* This is movl $,%eax ; int $0x80 */
+        /*
+         * This is movl $,%eax ; int $0x80
+         * This is no longer used, but is retained for ABI compatibility.
+         */
         __put_user(0xb8, (char *)(frame->retcode+0));
         __put_user(TARGET_NR_rt_sigreturn, (int *)(frame->retcode+1));
-        val16 = 0x80cd;
-        __put_user(val16, (uint16_t *)(frame->retcode+5));
+        __put_user(0x80cd, (uint16_t *)(frame->retcode+5));
+        retcode_addr = default_rt_sigreturn;
 #endif
     }
+    __put_user(retcode_addr, &frame->pretcode);
 
     /* Set up registers for signal handler */
     env->regs[R_ESP] = frame_addr;
diff --git a/linux-user/i386/Makefile.vdso b/linux-user/i386/Makefile.vdso
new file mode 100644
index 0000000000..42cfc1974b
--- /dev/null
+++ b/linux-user/i386/Makefile.vdso
@@ -0,0 +1,5 @@ 
+CROSS_CC ?= $(CC)
+
+vdso.so: vdso.S vdso.ld Makefile.vdso
+	$(CROSS_CC) -m32 -nostdlib -shared -Wl,-T,vdso.ld -Wl,--build-id=sha1 \
+	  -Wl,-h,linux-gate.so.1 -Wl,--hash-style=both vdso.S -o $@
diff --git a/linux-user/i386/meson.build b/linux-user/i386/meson.build
index ee523019a5..b729d73686 100644
--- a/linux-user/i386/meson.build
+++ b/linux-user/i386/meson.build
@@ -3,3 +3,10 @@  syscall_nr_generators += {
                     arguments: [ meson.current_source_dir() / 'syscallhdr.sh', '@INPUT@', '@OUTPUT@', '@EXTRA_ARGS@' ],
                     output: '@BASENAME@_nr.h')
 }
+
+gen = [
+  gen_vdso.process('vdso.so', extra_args: ['-s', '__kernel_sigreturn',
+                                           '-r', '__kernel_rt_sigreturn'])
+]
+
+linux_user_ss.add(when: 'TARGET_I386', if_true: gen)
diff --git a/linux-user/i386/vdso.S b/linux-user/i386/vdso.S
new file mode 100644
index 0000000000..6938c577ec
--- /dev/null
+++ b/linux-user/i386/vdso.S
@@ -0,0 +1,149 @@ 
+/*
+ * i386 linux replacement vdso.
+ *
+ * Copyright 2021 Linaro, Ltd.
+ * 
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+
+#include <asm/unistd.h>
+
+	.balign	16
+__kernel_vsyscall:
+	.cfi_startproc
+	int	$0x80
+	ret
+	.cfi_endproc
+
+	.globl	__kernel_vsyscall
+	.type	__kernel_vsyscall, @function
+	.size	__kernel_vsyscall, . - __kernel_vsyscall
+
+	.balign	16
+	.cfi_startproc
+__vdso_clock_gettime:
+	mov	$__NR_clock_gettime, %eax
+	int	$0x80
+	ret
+	.cfi_endproc
+
+	.globl	__vdso_clock_gettime
+	.type	__vdso_clock_gettime, @function
+	.size	__vdso_clock_gettime, . - __vdso_clock_gettime
+
+	.balign	16
+	.cfi_startproc
+__vdso_clock_gettime64:
+	mov	$__NR_clock_gettime64, %eax
+	int	$0x80
+	ret
+	.cfi_endproc
+
+	.globl	__vdso_clock_gettime64
+	.type	__vdso_clock_gettime64, @function
+	.size	__vdso_clock_gettime64, . - __vdso_clock_gettime64
+
+	.balign	16
+	.cfi_startproc
+__vdso_clock_getres:
+	mov	$__NR_clock_getres, %eax
+	int	$0x80
+	ret
+	.cfi_endproc
+
+	.globl	__vdso_clock_getres
+	.type	__vdso_clock_getres, @function
+	.size	__vdso_clock_getres, . - __vdso_clock_getres
+
+	.balign	16
+	.cfi_startproc
+__vdso_gettimeofday:
+	mov	$__NR_gettimeofday, %eax
+	int	$0x80
+	ret
+	.cfi_endproc
+
+	.globl	__vdso_gettimeofday
+	.type	__vdso_gettimeofday, @function
+	.size	__vdso_gettimeofday, . - __vdso_gettimeofday
+
+	.balign	16
+	.cfi_startproc
+__vdso_time:
+	mov	$__NR_time, %eax
+	int	$0x80
+	ret
+	.cfi_endproc
+
+	.globl	__vdso_time
+	.type	__vdso_time, @function
+	.size	__vdso_time, . - __vdso_time
+
+	/*
+	 * While this frame is marked as a signal frame, that only applies
+	 * to how this return address is handled for the outer frame.
+	 * The return address that arrived here, from the inner frame, is
+	 * not marked as a signal frame and so the unwinder still tries to
+	 * subtract 1 to examine the presumed call insn.  Thus we must
+	 * extend the unwind info to a nop before the start.
+	 */
+
+	.balign 16
+	.cfi_startproc simple
+	.cfi_signal_frame
+
+	/*
+	 * For convenience, put the cfa just above eip in sigcontext,
+	 * and count offsets backward from there.  Re-compute the cfa
+	 * in the several contexts we have for signal unwinding.
+         * This is far simpler than the DW_CFA_expression form that
+         * the kernel uses, and is equally correct.
+	 */
+#define IA32_SIGCONTEXT_cfa           60
+#define IA32_RT_SIGFRAME_sigcontext  164
+
+	.cfi_def_cfa	%esp, IA32_SIGCONTEXT_cfa + 4
+	.cfi_offset	%eip, -4
+			/* err, -8 */
+			/* trapno, -12 */
+	.cfi_offset	%eax, -16
+	.cfi_offset	%ecx, -20
+	.cfi_offset	%edx, -24
+	.cfi_offset	%ebx, -28
+	.cfi_offset	%esp, -32
+	.cfi_offset	%ebp, -36
+	.cfi_offset	%esi, -40
+	.cfi_offset	%edi, -44
+
+	nop
+__kernel_sigreturn:
+	popl	%eax	/* pop sig */
+	.cfi_adjust_cfa_offset -4
+	movl	$__NR_sigreturn, %eax
+	int	$0x80
+
+	.globl	__kernel_sigreturn
+	.type	__kernel_sigreturn, @function
+	.size	__kernel_sigreturn, . - __kernel_sigreturn
+
+	.cfi_adjust_cfa_offset IA32_RT_SIGFRAME_sigcontext - 4
+	nop
+__kernel_rt_sigreturn:
+	movl	$__NR_rt_sigreturn, %eax
+	int	$0x80
+
+	.globl	__kernel_rt_sigreturn
+	.type	__kernel_rt_sigreturn, @function
+	.size	__kernel_rt_sigreturn, . - __kernel_rt_sigreturn
+	.cfi_endproc
+
+/*
+ * ??? Perhaps add elf notes.  E.g.
+ *
+ * #include <linux/elfnote.h>
+ * ELFNOTE_START(Linux, 0, "a")
+ *   .long LINUX_VERSION_CODE
+ * ELFNOTE_END
+ *
+ * but what version number would we set for QEMU?
+ */
diff --git a/linux-user/i386/vdso.ld b/linux-user/i386/vdso.ld
new file mode 100644
index 0000000000..18937710c9
--- /dev/null
+++ b/linux-user/i386/vdso.ld
@@ -0,0 +1,76 @@ 
+/*
+ * Linker script for linux x86-64 replacement vdso.
+ *
+ * Copyright 2021 Linaro, Ltd.
+ * 
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+
+ENTRY(__kernel_vsyscall)
+
+VERSION {
+        LINUX_2.6 {
+        global:
+                __vdso_clock_gettime;
+                __vdso_gettimeofday;
+                __vdso_time;
+                __vdso_clock_getres;
+                __vdso_clock_gettime64;
+        };
+
+        LINUX_2.5 {
+        global:
+                __kernel_vsyscall;
+                __kernel_sigreturn;
+                __kernel_rt_sigreturn;
+        local: *;
+        };
+}
+
+PHDRS {
+        phdr            PT_PHDR         FLAGS(4) PHDRS;
+        data            PT_LOAD         FLAGS(6) FILEHDR PHDRS;
+        text            PT_LOAD         FLAGS(5);
+        dynamic         PT_DYNAMIC      FLAGS(4);
+        eh_frame_hdr    PT_GNU_EH_FRAME;
+        note            PT_NOTE         FLAGS(4);
+}
+
+SECTIONS {
+        /* ??? We can't really prelink to any address without knowing
+           something about the virtual memory space of the host, since
+           that leaks over into the available memory space of the guest.  */
+        . = SIZEOF_HEADERS;
+
+        /* The following, including the FILEHDRS and PHDRS, are modified
+           when we relocate the binary.  We want them to be initially
+           writable for the relocation; we'll force them read-only after.  */
+        .note           : { *(.note*) }         :data :note
+        .dynamic        : { *(.dynamic) }       :data :dynamic
+        .dynsym         : { *(.dynsym) }        :data
+        .data           : {
+                /* There ought not be any real read-write data.
+                   But since we manipulated the segment layout,
+                   we have to put these sections somewhere.  */
+                *(.data*)
+                *(.sdata*)
+                *(.got.plt) *(.got)
+                *(.gnu.linkonce.d.*)
+                *(.bss*)
+                *(.dynbss*)
+                *(.gnu.linkonce.b.*)
+        }
+
+        .rodata         : { *(.rodata*) }
+        .hash           : { *(.hash) }
+        .gnu.hash       : { *(.gnu.hash) }
+        .dynstr         : { *(.dynstr) }
+        .gnu.version    : { *(.gnu.version) }
+        .gnu.version_d  : { *(.gnu.version_d) }
+        .gnu.version_r  : { *(.gnu.version_r) }
+        .eh_frame_hdr   : { *(.eh_frame_hdr) }  :data :eh_frame_hdr
+        .eh_frame       : { *(.eh_frame) }      :data
+
+        . = ALIGN(4096);
+        .text           : { *(.text*) }         :text   =0x90909090
+}