[PATCH 17/22] Implement do_obreak function

[Karim Taha <kariem.taha2.7@gmail.com>]

From: Stacey Son <sson@FreeBSD.org>

Co-authored-by: Mikaël Urankar <mikael.urankar@gmail.com>

Signed-off-by: Mikaël Urankar <mikael.urankar@gmail.com>
Signed-off-by: Stacey Son <sson@FreeBSD.org>
Signed-off-by: Karim Taha <kariem.taha2.7@gmail.com>
---
 bsd-user/bsd-mem.h            | 85 +++++++++++++++++++++++++++++++++++
 bsd-user/freebsd/os-syscall.c |  7 +++
 2 files changed, 92 insertions(+)

diff --git a/bsd-user/bsd-mem.h b/bsd-user/bsd-mem.h
index edbccd3111..6f33148eb7 100644
--- a/bsd-user/bsd-mem.h
+++ b/bsd-user/bsd-mem.h
@@ -167,4 +167,89 @@ static inline abi_long do_bsd_mincore(abi_ulong target_addr, abi_ulong len,
     return ret;
 }
 
+#ifdef DO_DEBUG
+#define DEBUGF_BRK(message, args...) \
+    do { fprintf(stderr, (message), ## args); } while (0)
+#else
+#define DEBUGF_BRK(message, args...)
+#endif
+
+/* do_brk() must return target values and target errnos. */
+static inline abi_long do_obreak(abi_ulong new_brk)
+{
+    abi_long mapped_addr;
+    int new_alloc_size;
+
+    DEBUGF_BRK("do_brk(" TARGET_ABI_FMT_lx ") -> ", new_brk);
+
+    if (!new_brk) {
+        DEBUGF_BRK(TARGET_ABI_FMT_lx " (!new_brk)\n", bsd_target_brk);
+        return bsd_target_brk;
+    }
+    if (new_brk < bsd_target_original_brk) {
+        DEBUGF_BRK(TARGET_ABI_FMT_lx " (new_brk < bsd_target_original_brk)\n",
+                   bsd_target_brk);
+        return bsd_target_brk;
+    }
+
+    /*
+     * If the new brk is less than the highest page reserved to the target heap
+     * allocation, set it and we're almost done...
+     */
+    if (new_brk <= brk_page) {
+        /*
+         * Heap contents are initialized to zero, as for anonymous mapped pages.
+         */
+        if (new_brk > bsd_target_brk) {
+            memset(g2h_untagged(bsd_target_brk), 0, new_brk - bsd_target_brk);
+        }
+        bsd_target_brk = new_brk;
+        DEBUGF_BRK(TARGET_ABI_FMT_lx " (new_brk <= brk_page)\n",
+                   bsd_target_brk);
+        return bsd_target_brk;
+    }
+
+    /*
+     * We need to allocate more memory after the brk... Note that we don't use
+     * MAP_FIXED because that will map over the top of any existing mapping
+     * (like the one with the host libc or qemu itself); instead we treat
+     * "mapped but at wrong address" as a failure and unmap again.
+     */
+    new_alloc_size = HOST_PAGE_ALIGN(new_brk - brk_page);
+    mapped_addr = get_errno(target_mmap(brk_page, new_alloc_size,
+                                        PROT_READ | PROT_WRITE,
+                                        MAP_ANON | MAP_PRIVATE, -1, 0));
+
+    if (mapped_addr == brk_page) {
+        /*
+         * Heap contents are initialized to zero, as for anonymous mapped pages.
+         * Technically the new pages are already initialized to zero since they
+         * *are* anonymous mapped pages, however we have to take care with the
+         * contents that come from the remaining part of the previous page: it
+         * may contains garbage data due to a previous heap usage (grown then
+         * shrunken).
+         */
+        memset(g2h_untagged(bsd_target_brk), 0, brk_page - bsd_target_brk);
+
+        bsd_target_brk = new_brk;
+        brk_page = HOST_PAGE_ALIGN(bsd_target_brk);
+        DEBUGF_BRK(TARGET_ABI_FMT_lx " (mapped_addr == brk_page)\n",
+            bsd_target_brk);
+        return bsd_target_brk;
+    } else if (mapped_addr != -1) {
+        /*
+         * Mapped but at wrong address, meaning there wasn't actually enough
+         * space for this brk.
+         */
+        target_munmap(mapped_addr, new_alloc_size);
+        mapped_addr = -1;
+        DEBUGF_BRK(TARGET_ABI_FMT_lx " (mapped_addr != -1)\n", bsd_target_brk);
+    } else {
+        DEBUGF_BRK(TARGET_ABI_FMT_lx " (otherwise)\n", bsd_target_brk);
+    }
+
+    /* For everything else, return the previous break. */
+    return bsd_target_brk;
+}
+
 #endif /* BSD_USER_BSD_MEM_H */
diff --git a/bsd-user/freebsd/os-syscall.c b/bsd-user/freebsd/os-syscall.c
index 1db0907504..1b9dca9164 100644
--- a/bsd-user/freebsd/os-syscall.c
+++ b/bsd-user/freebsd/os-syscall.c
@@ -543,6 +543,13 @@ static abi_long freebsd_syscall(void *cpu_env, int num, abi_long arg1,
         break;
 #endif
 
+        /*
+         * Misc
+         */
+    case TARGET_FREEBSD_NR_break:
+        ret = do_obreak(arg1);
+        break;
+
         /*
          * sys{ctl, arch, call}
          */
-- 
2.40.0