linux-user: completely re-write init_guest_space

First we ensure all guest space initialisation logic comes through
probe_guest_base once we understand the nature of the binary we are
loading. The convoluted init_guest_space routine is removed and
replaced with a number of pgb_* helpers which are called depending on
what requirements we have when loading the binary.

We first try to do what is requested by the host. Failing that we try
and satisfy the guest requested base address. If all those options
fail we fall back to finding a space in the memory map using our
recently written read_self_maps() helper.

There are some additional complications we try and take into account
when looking for holes in the address space. We try not to go directly
after the system brk() space so there is space for a little growth. We
also don't want to have to use negative offsets which would result in
slightly less efficient code on x86 when it's unable to use the
segment offset register.

Less mind-binding gotos and hopefully clearer logic throughout.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Acked-by: Laurent Vivier <laurent@vivier.eu>

Message-Id: <20200513175134.19619-5-alex.bennee@linaro.org>

1 files changed, 20 insertions, 11 deletions

diff --git a/linux-user/qemu.h b/linux-user/qemu.h
index 792c74290f..ce902f5132 100644
--- a/linux-user/qemu.h
+++ b/linux-user/qemu.h
@@ -219,18 +219,27 @@ void init_qemu_uname_release(void);
 void fork_start(void);
 void fork_end(int child);
 
-/* Creates the initial guest address space in the host memory space using
- * the given host start address hint and size.  The guest_start parameter
- * specifies the start address of the guest space.  guest_base will be the
- * difference between the host start address computed by this function and
- * guest_start.  If fixed is specified, then the mapped address space must
- * start at host_start.  The real start address of the mapped memory space is
- * returned or -1 if there was an error.
+/**
+ * probe_guest_base:
+ * @image_name: the executable being loaded
+ * @loaddr: the lowest fixed address in the executable
+ * @hiaddr: the highest fixed address in the executable
+ *
+ * Creates the initial guest address space in the host memory space.
+ *
+ * If @loaddr == 0, then no address in the executable is fixed,
+ * i.e. it is fully relocatable.  In that case @hiaddr is the size
+ * of the executable.
+ *
+ * This function will not return if a valid value for guest_base
+ * cannot be chosen.  On return, the executable loader can expect
+ *
+ *    target_mmap(loaddr, hiaddr - loaddr, ...)
+ *
+ * to succeed.
  */
-unsigned long init_guest_space(unsigned long host_start,
-                               unsigned long host_size,
-                               unsigned long guest_start,
-                               bool fixed);
+void probe_guest_base(const char *image_name,
+                      abi_ulong loaddr, abi_ulong hiaddr);
 
 #include "qemu/log.h"