[PATCH v4 0/3] user: Extract common MMAP API to 'user/mmap.h'

[PATCH v4 0/3] user: Extract common MMAP API to 'user/mmap.h'

[Philippe Mathieu-Daudé]

Since v2:
- Addressed rth's comments

Since v1:
- Propagate alignment argument to BSD's mmap_find_vma()

Philippe Mathieu-Daudé (3):
  bsd-user: Always use mmap_find_vma_aligned() in target_mmap()
  bsd-user: Propagate alignment argument to mmap_find_vma()
  user: Extract common MMAP API to 'user/mmap.h'

 bsd-user/bsd-mem.h     |  4 +++-
 bsd-user/qemu.h        | 12 +-----------
 include/user/mmap.h    | 32 ++++++++++++++++++++++++++++++++
 linux-user/user-mmap.h | 19 ++-----------------
 bsd-user/mmap.c        | 17 +++++------------
 5 files changed, 43 insertions(+), 41 deletions(-)
 create mode 100644 include/user/mmap.h

-- 
2.47.1

[PATCH v4 1/3] bsd-user: Always use mmap_find_vma_aligned() in target_mmap()

[Philippe Mathieu-Daudé]

Massage target_mmap(): calculate alignment once, then
unconditionally call mmap_find_vma_aligned().

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
---
 bsd-user/mmap.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/bsd-user/mmap.c b/bsd-user/mmap.c
index 346f2cefd32..dfa6e728ab5 100644
--- a/bsd-user/mmap.c
+++ b/bsd-user/mmap.c
@@ -489,13 +489,12 @@ abi_long target_mmap(abi_ulong start, abi_ulong len, int prot,
      * before we truncate the length for mapping files below.
      */
     if (!(flags & MAP_FIXED)) {
+        abi_ulong alignment;
+
         host_len = len + offset - host_offset;
         host_len = HOST_PAGE_ALIGN(host_len);
-        if ((flags & MAP_ALIGNMENT_MASK) != 0)
-            start = mmap_find_vma_aligned(real_start, host_len,
-                (flags & MAP_ALIGNMENT_MASK) >> MAP_ALIGNMENT_SHIFT);
-        else
-            start = mmap_find_vma(real_start, host_len);
+        alignment = (flags & MAP_ALIGNMENT_MASK) >> MAP_ALIGNMENT_SHIFT;
+        start = mmap_find_vma_aligned(real_start, host_len, alignment);
         if (start == (abi_ulong)-1) {
             errno = ENOMEM;
             goto fail;
-- 
2.47.1

Re: [PATCH v4 1/3] bsd-user: Always use mmap_find_vma_aligned() in target_mmap()

[Warner Losh]

[-- Attachment #1: Type: text/plain, Size: 1590 bytes --]

On Sat, Mar 8, 2025 at 5:28 AM Philippe Mathieu-Daudé <philmd@linaro.org>
wrote:

> Massage target_mmap(): calculate alignment once, then
> unconditionally call mmap_find_vma_aligned().
>
> Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
> Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
> ---
>  bsd-user/mmap.c | 9 ++++-----
>  1 file changed, 4 insertions(+), 5 deletions(-)
>

Reviewed-by: Warner Losh <imp@bsdimp.com>

Here I get why you have a new variable since it's a  little easier to read.

Warner


> diff --git a/bsd-user/mmap.c b/bsd-user/mmap.c
> index 346f2cefd32..dfa6e728ab5 100644
> --- a/bsd-user/mmap.c
> +++ b/bsd-user/mmap.c
> @@ -489,13 +489,12 @@ abi_long target_mmap(abi_ulong start, abi_ulong len,
> int prot,
>       * before we truncate the length for mapping files below.
>       */
>      if (!(flags & MAP_FIXED)) {
> +        abi_ulong alignment;
> +
>          host_len = len + offset - host_offset;
>          host_len = HOST_PAGE_ALIGN(host_len);
> -        if ((flags & MAP_ALIGNMENT_MASK) != 0)
> -            start = mmap_find_vma_aligned(real_start, host_len,
> -                (flags & MAP_ALIGNMENT_MASK) >> MAP_ALIGNMENT_SHIFT);
> -        else
> -            start = mmap_find_vma(real_start, host_len);
> +        alignment = (flags & MAP_ALIGNMENT_MASK) >> MAP_ALIGNMENT_SHIFT;
> +        start = mmap_find_vma_aligned(real_start, host_len, alignment);
>          if (start == (abi_ulong)-1) {
>              errno = ENOMEM;
>              goto fail;
> --
> 2.47.1
>
>

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[PATCH v4 2/3] bsd-user: Propagate alignment argument to mmap_find_vma()

[Philippe Mathieu-Daudé]

Propagate the alignment to mmap_find_vma(), effectively
embedding mmap_find_vma_aligned() within mmap_find_vma().

Add a comment in do_bsd_shmat() to clarify alignment above
page size is not required.

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
---
 bsd-user/bsd-mem.h |  4 +++-
 bsd-user/qemu.h    |  2 +-
 bsd-user/mmap.c    | 10 ++--------
 3 files changed, 6 insertions(+), 10 deletions(-)

diff --git a/bsd-user/bsd-mem.h b/bsd-user/bsd-mem.h
index f5ec0de24ca..90ca0e33775 100644
--- a/bsd-user/bsd-mem.h
+++ b/bsd-user/bsd-mem.h
@@ -370,9 +370,11 @@ static inline abi_long do_bsd_shmat(int shmid, abi_ulong shmaddr, int shmflg)
         if (shmaddr) {
             host_raddr = shmat(shmid, (void *)g2h_untagged(shmaddr), shmflg);
         } else {
+            abi_ulong alignment;
             abi_ulong mmap_start;
 
-            mmap_start = mmap_find_vma(0, shm_info.shm_segsz);
+            alignment = 0; /* alignment above page size not required */
+            mmap_start = mmap_find_vma(0, shm_info.shm_segsz, alignment);
 
             if (mmap_start == -1) {
                 return -TARGET_ENOMEM;
diff --git a/bsd-user/qemu.h b/bsd-user/qemu.h
index 4e97c796318..0b3bd65b180 100644
--- a/bsd-user/qemu.h
+++ b/bsd-user/qemu.h
@@ -242,7 +242,7 @@ abi_long target_mremap(abi_ulong old_addr, abi_ulong old_size,
                        abi_ulong new_addr);
 int target_msync(abi_ulong start, abi_ulong len, int flags);
 extern abi_ulong mmap_next_start;
-abi_ulong mmap_find_vma(abi_ulong start, abi_ulong size);
+abi_ulong mmap_find_vma(abi_ulong start, abi_ulong size, abi_ulong alignment);
 void mmap_reserve(abi_ulong start, abi_ulong size);
 void TSA_NO_TSA mmap_fork_start(void);
 void TSA_NO_TSA mmap_fork_end(int child);
diff --git a/bsd-user/mmap.c b/bsd-user/mmap.c
index dfa6e728ab5..3f0df79c375 100644
--- a/bsd-user/mmap.c
+++ b/bsd-user/mmap.c
@@ -275,8 +275,7 @@ static abi_ulong mmap_find_vma_reserved(abi_ulong start, abi_ulong size,
  * It must be called with mmap_lock() held.
  * Return -1 if error.
  */
-static abi_ulong mmap_find_vma_aligned(abi_ulong start, abi_ulong size,
-                                       abi_ulong alignment)
+abi_ulong mmap_find_vma(abi_ulong start, abi_ulong size, abi_ulong alignment)
 {
     void *ptr, *prev;
     abi_ulong addr;
@@ -395,11 +394,6 @@ static abi_ulong mmap_find_vma_aligned(abi_ulong start, abi_ulong size,
     }
 }
 
-abi_ulong mmap_find_vma(abi_ulong start, abi_ulong size)
-{
-    return mmap_find_vma_aligned(start, size, 0);
-}
-
 /* NOTE: all the constants are the HOST ones */
 abi_long target_mmap(abi_ulong start, abi_ulong len, int prot,
                      int flags, int fd, off_t offset)
@@ -494,7 +488,7 @@ abi_long target_mmap(abi_ulong start, abi_ulong len, int prot,
         host_len = len + offset - host_offset;
         host_len = HOST_PAGE_ALIGN(host_len);
         alignment = (flags & MAP_ALIGNMENT_MASK) >> MAP_ALIGNMENT_SHIFT;
-        start = mmap_find_vma_aligned(real_start, host_len, alignment);
+        start = mmap_find_vma(real_start, host_len, alignment);
         if (start == (abi_ulong)-1) {
             errno = ENOMEM;
             goto fail;
-- 
2.47.1

Re: [PATCH v4 2/3] bsd-user: Propagate alignment argument to mmap_find_vma()

[Warner Losh]

[-- Attachment #1: Type: text/plain, Size: 3867 bytes --]

On Sat, Mar 8, 2025 at 5:28 AM Philippe Mathieu-Daudé <philmd@linaro.org>
wrote:

> Propagate the alignment to mmap_find_vma(), effectively
> embedding mmap_find_vma_aligned() within mmap_find_vma().
>
> Add a comment in do_bsd_shmat() to clarify alignment above
> page size is not required.
>
> Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
> ---
>  bsd-user/bsd-mem.h |  4 +++-
>  bsd-user/qemu.h    |  2 +-
>  bsd-user/mmap.c    | 10 ++--------
>  3 files changed, 6 insertions(+), 10 deletions(-)
>

Reviewed-by: Warner Losh <imp@bsdimp.com>


> diff --git a/bsd-user/bsd-mem.h b/bsd-user/bsd-mem.h
> index f5ec0de24ca..90ca0e33775 100644
> --- a/bsd-user/bsd-mem.h
> +++ b/bsd-user/bsd-mem.h
> @@ -370,9 +370,11 @@ static inline abi_long do_bsd_shmat(int shmid,
> abi_ulong shmaddr, int shmflg)
>          if (shmaddr) {
>              host_raddr = shmat(shmid, (void *)g2h_untagged(shmaddr),
> shmflg);
>          } else {
> +            abi_ulong alignment;
>              abi_ulong mmap_start;
>
> -            mmap_start = mmap_find_vma(0, shm_info.shm_segsz);
> +            alignment = 0; /* alignment above page size not required */
> +            mmap_start = mmap_find_vma(0, shm_info.shm_segsz, alignment);
>

Why create a write-only variable that you just pass to this function? Is
this
a pattern used elsewhere and if so when?

It's fine, imho, like this, but it is a little odd so I wonder why you did
it like this.
There may be something I can learn.

Warner


>              if (mmap_start == -1) {
>                  return -TARGET_ENOMEM;
> diff --git a/bsd-user/qemu.h b/bsd-user/qemu.h
> index 4e97c796318..0b3bd65b180 100644
> --- a/bsd-user/qemu.h
> +++ b/bsd-user/qemu.h
> @@ -242,7 +242,7 @@ abi_long target_mremap(abi_ulong old_addr, abi_ulong
> old_size,
>                         abi_ulong new_addr);
>  int target_msync(abi_ulong start, abi_ulong len, int flags);
>  extern abi_ulong mmap_next_start;
> -abi_ulong mmap_find_vma(abi_ulong start, abi_ulong size);
> +abi_ulong mmap_find_vma(abi_ulong start, abi_ulong size, abi_ulong
> alignment);
>  void mmap_reserve(abi_ulong start, abi_ulong size);
>  void TSA_NO_TSA mmap_fork_start(void);
>  void TSA_NO_TSA mmap_fork_end(int child);
> diff --git a/bsd-user/mmap.c b/bsd-user/mmap.c
> index dfa6e728ab5..3f0df79c375 100644
> --- a/bsd-user/mmap.c
> +++ b/bsd-user/mmap.c
> @@ -275,8 +275,7 @@ static abi_ulong mmap_find_vma_reserved(abi_ulong
> start, abi_ulong size,
>   * It must be called with mmap_lock() held.
>   * Return -1 if error.
>   */
> -static abi_ulong mmap_find_vma_aligned(abi_ulong start, abi_ulong size,
> -                                       abi_ulong alignment)
> +abi_ulong mmap_find_vma(abi_ulong start, abi_ulong size, abi_ulong
> alignment)
>  {
>      void *ptr, *prev;
>      abi_ulong addr;
> @@ -395,11 +394,6 @@ static abi_ulong mmap_find_vma_aligned(abi_ulong
> start, abi_ulong size,
>      }
>  }
>
> -abi_ulong mmap_find_vma(abi_ulong start, abi_ulong size)
> -{
> -    return mmap_find_vma_aligned(start, size, 0);
> -}
> -
>  /* NOTE: all the constants are the HOST ones */
>  abi_long target_mmap(abi_ulong start, abi_ulong len, int prot,
>                       int flags, int fd, off_t offset)
> @@ -494,7 +488,7 @@ abi_long target_mmap(abi_ulong start, abi_ulong len,
> int prot,
>          host_len = len + offset - host_offset;
>          host_len = HOST_PAGE_ALIGN(host_len);
>          alignment = (flags & MAP_ALIGNMENT_MASK) >> MAP_ALIGNMENT_SHIFT;
> -        start = mmap_find_vma_aligned(real_start, host_len, alignment);
> +        start = mmap_find_vma(real_start, host_len, alignment);
>          if (start == (abi_ulong)-1) {
>              errno = ENOMEM;
>              goto fail;
> --
> 2.47.1
>
>

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[PATCH v4 3/3] user: Extract common MMAP API to 'user/mmap.h'

[Philippe Mathieu-Daudé]

Keep common MMAP-related declarations in a single place.

Note, this disable ThreadSafetyAnalysis on Linux for:
- mmap_fork_start()
- mmap_fork_end().

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Warner Losh <imp@bsdimp.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
---
 bsd-user/qemu.h        | 12 +-----------
 include/user/mmap.h    | 32 ++++++++++++++++++++++++++++++++
 linux-user/user-mmap.h | 19 ++-----------------
 3 files changed, 35 insertions(+), 28 deletions(-)
 create mode 100644 include/user/mmap.h

diff --git a/bsd-user/qemu.h b/bsd-user/qemu.h
index 0b3bd65b180..c1c508281a8 100644
--- a/bsd-user/qemu.h
+++ b/bsd-user/qemu.h
@@ -32,6 +32,7 @@
 extern char **environ;
 
 #include "user/thunk.h"
+#include "user/mmap.h"
 #include "target_arch.h"
 #include "syscall_defs.h"
 #include "target_syscall.h"
@@ -233,19 +234,8 @@ void print_taken_signal(int target_signum, const target_siginfo_t *tinfo);
 extern int do_strace;
 
 /* mmap.c */
-int target_mprotect(abi_ulong start, abi_ulong len, int prot);
-abi_long target_mmap(abi_ulong start, abi_ulong len, int prot,
-                     int flags, int fd, off_t offset);
-int target_munmap(abi_ulong start, abi_ulong len);
-abi_long target_mremap(abi_ulong old_addr, abi_ulong old_size,
-                       abi_ulong new_size, unsigned long flags,
-                       abi_ulong new_addr);
 int target_msync(abi_ulong start, abi_ulong len, int flags);
-extern abi_ulong mmap_next_start;
-abi_ulong mmap_find_vma(abi_ulong start, abi_ulong size, abi_ulong alignment);
 void mmap_reserve(abi_ulong start, abi_ulong size);
-void TSA_NO_TSA mmap_fork_start(void);
-void TSA_NO_TSA mmap_fork_end(int child);
 
 /* main.c */
 extern char qemu_proc_pathname[];
diff --git a/include/user/mmap.h b/include/user/mmap.h
new file mode 100644
index 00000000000..4d5e9aac70a
--- /dev/null
+++ b/include/user/mmap.h
@@ -0,0 +1,32 @@
+/*
+ * MMAP declarations for QEMU user emulation
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+#ifndef USER_MMAP_H
+#define USER_MMAP_H
+
+#include "user/abitypes.h"
+
+/*
+ * mmap_next_start: The base address for the next mmap without hint,
+ * increased after each successful map, starting at task_unmapped_base.
+ * This is an optimization within QEMU and not part of ADDR_COMPAT_LAYOUT.
+ */
+extern abi_ulong mmap_next_start;
+
+int target_mprotect(abi_ulong start, abi_ulong len, int prot);
+
+abi_long target_mmap(abi_ulong start, abi_ulong len, int prot,
+                     int flags, int fd, off_t offset);
+int target_munmap(abi_ulong start, abi_ulong len);
+abi_long target_mremap(abi_ulong old_addr, abi_ulong old_size,
+                       abi_ulong new_size, unsigned long flags,
+                       abi_ulong new_addr);
+
+abi_ulong mmap_find_vma(abi_ulong start, abi_ulong size, abi_ulong alignment);
+
+void TSA_NO_TSA mmap_fork_start(void);
+void TSA_NO_TSA mmap_fork_end(int child);
+
+#endif
diff --git a/linux-user/user-mmap.h b/linux-user/user-mmap.h
index b94bcdcf83c..dfc4477a720 100644
--- a/linux-user/user-mmap.h
+++ b/linux-user/user-mmap.h
@@ -18,6 +18,8 @@
 #ifndef LINUX_USER_USER_MMAP_H
 #define LINUX_USER_USER_MMAP_H
 
+#include "user/mmap.h"
+
 /*
  * Guest parameters for the ADDR_COMPAT_LAYOUT personality
  * (at present this is the only layout supported by QEMU).
@@ -39,24 +41,7 @@
 extern abi_ulong task_unmapped_base;
 extern abi_ulong elf_et_dyn_base;
 
-/*
- * mmap_next_start: The base address for the next mmap without hint,
- * increased after each successful map, starting at task_unmapped_base.
- * This is an optimization within QEMU and not part of ADDR_COMPAT_LAYOUT.
- */
-extern abi_ulong mmap_next_start;
-
-int target_mprotect(abi_ulong start, abi_ulong len, int prot);
-abi_long target_mmap(abi_ulong start, abi_ulong len, int prot,
-                     int flags, int fd, off_t offset);
-int target_munmap(abi_ulong start, abi_ulong len);
-abi_long target_mremap(abi_ulong old_addr, abi_ulong old_size,
-                       abi_ulong new_size, unsigned long flags,
-                       abi_ulong new_addr);
 abi_long target_madvise(abi_ulong start, abi_ulong len_in, int advice);
-abi_ulong mmap_find_vma(abi_ulong, abi_ulong, abi_ulong);
-void mmap_fork_start(void);
-void mmap_fork_end(int child);
 
 abi_ulong target_shmat(CPUArchState *cpu_env, int shmid,
                        abi_ulong shmaddr, int shmflg);
-- 
2.47.1

Re: [PATCH v4 0/3] user: Extract common MMAP API to 'user/mmap.h'

[Philippe Mathieu-Daudé]

On 8/3/25 13:28, Philippe Mathieu-Daudé wrote:

> Philippe Mathieu-Daudé (3):
>    bsd-user: Always use mmap_find_vma_aligned() in target_mmap()
>    bsd-user: Propagate alignment argument to mmap_find_vma()
>    user: Extract common MMAP API to 'user/mmap.h'

Series queued, thanks.