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Re: [PATCH v6 09/19] linux-user/i386: Add vdso


From: Philippe Mathieu-Daudé
Subject: Re: [PATCH v6 09/19] linux-user/i386: Add vdso
Date: Thu, 5 Oct 2023 18:42:20 +0200
User-agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:102.0) Gecko/20100101 Thunderbird/102.15.1

On 30/9/23 04:15, Richard Henderson wrote:
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1267
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
  linux-user/i386/vdso-asmoffset.h |   6 ++
  linux-user/elfload.c             |  19 +++-
  linux-user/i386/signal.c         |  11 +++
  linux-user/i386/Makefile.vdso    |  11 +++
  linux-user/i386/meson.build      |   7 ++
  linux-user/i386/vdso.S           | 143 +++++++++++++++++++++++++++++++
  linux-user/i386/vdso.ld          |  76 ++++++++++++++++
  linux-user/i386/vdso.so          | Bin 0 -> 2672 bytes
  8 files changed, 271 insertions(+), 2 deletions(-)
  create mode 100644 linux-user/i386/vdso-asmoffset.h
  create mode 100644 linux-user/i386/Makefile.vdso
  create mode 100644 linux-user/i386/vdso.S
  create mode 100644 linux-user/i386/vdso.ld
  create mode 100755 linux-user/i386/vdso.so

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>

diff --git a/linux-user/i386/vdso-asmoffset.h b/linux-user/i386/vdso-asmoffset.h
new file mode 100644
index 0000000000..4e5ee0dd49
--- /dev/null
+++ b/linux-user/i386/vdso-asmoffset.h
@@ -0,0 +1,6 @@
+/*
+ * offsetof(struct sigframe, sc.eip)
+ * offsetof(struct rt_sigframe, uc.tuc_mcontext.eip)
+ */
+#define SIGFRAME_SIGCONTEXT_eip      64
+#define RT_SIGFRAME_SIGCONTEXT_eip  220
diff --git a/linux-user/elfload.c b/linux-user/elfload.c
index 9c97d14b7e..314ae7cacf 100644
--- a/linux-user/elfload.c
+++ b/linux-user/elfload.c
@@ -305,12 +305,27 @@ static void elf_core_copy_regs(target_elf_gregset_t 
*regs, const CPUX86State *en
      (*regs)[15] = tswapreg(env->regs[R_ESP]);
      (*regs)[16] = tswapreg(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 (vdso_info != NULL)
+#define ARCH_DLINFO                                     \
+    do {                                                \
+        if (vdso_info) {                                \
+            NEW_AUX_ENT(AT_SYSINFO, vdso_info->entry);  \
+        }                                               \
+    } while (0)
+
+#define VDSO_HEADER "vdso.c.inc"
+
+#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 60fa07d6f9..bc5d45302e 100644
--- a/linux-user/i386/signal.c
+++ b/linux-user/i386/signal.c
@@ -214,6 +214,17 @@ struct rt_sigframe {
  };
  #define TARGET_RT_SIGFRAME_FXSAVE_OFFSET (                                 \
      offsetof(struct rt_sigframe, fpstate) + TARGET_FPSTATE_FXSAVE_OFFSET)
+
+/*
+ * Verify that vdso-asmoffset.h constants match.
+ */
+#include "i386/vdso-asmoffset.h"
+
+QEMU_BUILD_BUG_ON(offsetof(struct sigframe, sc.eip)
+                  != SIGFRAME_SIGCONTEXT_eip);
+QEMU_BUILD_BUG_ON(offsetof(struct rt_sigframe, uc.tuc_mcontext.eip)
+                  != RT_SIGFRAME_SIGCONTEXT_eip);
+
  #else
struct rt_sigframe {
diff --git a/linux-user/i386/Makefile.vdso b/linux-user/i386/Makefile.vdso
new file mode 100644
index 0000000000..95bc616f6d
--- /dev/null
+++ b/linux-user/i386/Makefile.vdso
@@ -0,0 +1,11 @@
+include $(BUILD_DIR)/tests/tcg/i386-linux-user/config-target.mak
+
+SUBDIR = $(SRC_PATH)/linux-user/i386
+VPATH += $(SUBDIR)
+
+all: $(SUBDIR)/vdso.so
+
+$(SUBDIR)/vdso.so: vdso.S vdso.ld vdso-asmoffset.h
+       $(CC) -o $@ -m32 -nostdlib -shared -Wl,-h,linux-gate.so.1 \
+         -Wl,--build-id=sha1 -Wl,--hash-style=both \
+         -Wl,-T,$(SUBDIR)/vdso.ld $<
diff --git a/linux-user/i386/meson.build b/linux-user/i386/meson.build
index ee523019a5..d42fc6cbc9 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')
  }
+
+vdso_inc = gen_vdso.process('vdso.so', extra_args: [
+                                '-s', '__kernel_sigreturn',
+                                '-r', '__kernel_rt_sigreturn'
+                            ])
+
+linux_user_ss.add(when: 'TARGET_I386', if_true: vdso_inc)
diff --git a/linux-user/i386/vdso.S b/linux-user/i386/vdso.S
new file mode 100644
index 0000000000..e7a1f333a1
--- /dev/null
+++ b/linux-user/i386/vdso.S
@@ -0,0 +1,143 @@
+/*
+ * i386 linux replacement vdso.
+ *
+ * Copyright 2023 Linaro, Ltd.
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+
+#include <asm/unistd.h>
+#include "vdso-asmoffset.h"
+
+.macro endf name
+       .globl  \name
+       .type   \name, @function
+       .size   \name, . - \name
+.endm
+
+.macro vdso_syscall1 name, nr
+\name:
+       .cfi_startproc
+       mov     %ebx, %edx
+       .cfi_register %ebx, %edx
+       mov     4(%esp), %ebx
+       mov     $\nr, %eax
+       int     $0x80
+       mov     %edx, %ebx
+       ret
+       .cfi_endproc
+endf   \name
+.endm
+
+.macro vdso_syscall2 name, nr
+\name:
+       .cfi_startproc
+       mov     %ebx, %edx
+       .cfi_register %ebx, %edx
+       mov     4(%esp), %ebx
+       mov     8(%esp), %ecx
+       mov     $\nr, %eax
+       int     $0x80
+       mov     %edx, %ebx
+       ret
+       .cfi_endproc
+endf   \name
+.endm
+
+.macro vdso_syscall3 name, nr
+\name:
+       .cfi_startproc
+       push    %ebx
+       .cfi_adjust_cfa_offset 4
+       .cfi_rel_offset %ebx, 0
+       mov     8(%esp), %ebx
+       mov     12(%esp), %ecx
+       mov     16(%esp), %edx
+       mov     $\nr, %eax
+       int     $0x80
+       pop     %ebx
+       .cfi_adjust_cfa_offset -4
+       .cfi_restore %ebx
+       ret
+       .cfi_endproc
+endf   \name
+.endm
+
+__kernel_vsyscall:
+       .cfi_startproc
+       int     $0x80
+       ret
+       .cfi_endproc
+endf   __kernel_vsyscall
+
+vdso_syscall2 __vdso_clock_gettime, __NR_clock_gettime
+vdso_syscall2 __vdso_clock_gettime64, __NR_clock_gettime64
+vdso_syscall2 __vdso_clock_getres, __NR_clock_getres
+vdso_syscall2 __vdso_gettimeofday, __NR_gettimeofday
+vdso_syscall1 __vdso_time, __NR_time
+vdso_syscall3 __vdso_getcpu, __NR_gettimeofday
+
+/*
+ * Signal return handlers.
+ */
+
+       .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 two contexts
+ * we have for signal unwinding.  This is far simpler than the
+ * DW_CFA_expression form that the kernel uses, and is equally correct.
+ */
+
+       .cfi_def_cfa    %esp, SIGFRAME_SIGCONTEXT_eip + 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
+
+/*
+ * While this frame is marked as a signal frame, that only applies to how
+ * the 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.
+ */
+       nop
+
+__kernel_sigreturn:
+       popl    %eax    /* pop sig */
+       .cfi_adjust_cfa_offset -4
+       movl    $__NR_sigreturn, %eax
+       int     $0x80
+endf   __kernel_sigreturn
+
+       .cfi_def_cfa_offset RT_SIGFRAME_SIGCONTEXT_eip + 4
+       nop
+
+__kernel_rt_sigreturn:
+       movl    $__NR_rt_sigreturn, %eax
+       int     $0x80
+endf   __kernel_rt_sigreturn
+
+       .cfi_endproc
+
+/*
+ * TODO: 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..326b7a8f98
--- /dev/null
+++ b/linux-user/i386/vdso.ld
@@ -0,0 +1,76 @@
+/*
+ * Linker script for linux i386 replacement vdso.
+ *
+ * Copyright 2023 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;
+                __vdso_getcpu;
+        };
+
+        LINUX_2.5 {
+        global:
+                __kernel_vsyscall;
+                __kernel_sigreturn;
+                __kernel_rt_sigreturn;
+        local: *;
+        };
+}
+
+PHDRS {
+        phdr            PT_PHDR         FLAGS(4) PHDRS;
+        load            PT_LOAD         FLAGS(7) FILEHDR PHDRS; /* FLAGS=RWX */
+        dynamic         PT_DYNAMIC      FLAGS(4);
+        eh_frame_hdr    PT_GNU_EH_FRAME;
+        note            PT_NOTE         FLAGS(4);
+}
+
+SECTIONS {
+        . = 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*) }         :load :note
+        .dynamic        : { *(.dynamic) }       :load :dynamic
+        .dynsym         : { *(.dynsym) }        :load
+        .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) }  :load :eh_frame_hdr
+        .eh_frame       : { *(.eh_frame) }      :load
+
+        .text           : { *(.text*) }         :load   =0x90909090
+}
diff --git a/linux-user/i386/vdso.so b/linux-user/i386/vdso.so
new file mode 100755
index 
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GIT binary patch
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